Tungsten oxide nanostructure thin films for electrochromic devices

ABSTRACT

A method of manufacturing a thin film is provided. The method includes providing a plurality of crystalline hexagonal tungsten trioxide particles, size-reducing the crystalline hexagonal tungsten trioxide particles by grinding to produce crystalline hexagonal tungsten trioxide nanostructures, and coating the crystalline hexagonal tungsten trioxide nanostructures onto a substrate to produce a thin film. An electrochromic multi-layer stack is also provided.

FIELD OF INVENTION

The present disclosure generally relates to thin films of tungsten oxideand tungsten trioxide nanostructures and the substituted versions ofeach and methods for preparing the nanostructures, thin films,electrochromic multi-layer stacks and electrochromic devices. Thisdisclosure also relates to the different phases of tungsten oxide ortrioxide nanostructures including monoclinic, triclinic, orthorhombic,tetragonal, and hexagonal.

BACKGROUND

Tungsten oxide materials are useful for their electrochemical andelectrochromic behavior, and they are widely used in electrochromicdevices. There are a number of different deposition techniques andpolymorphs of tungsten oxide that have been used in electrochromicdevices. Amorphous tungsten trioxide deposited by either thermalevaporation or sol-gel methods, is often used for electrochromicapplications although crystalline tungsten trioxide is also used.

Commercial switchable glazing devices, also commonly known as smartwindows and electrochromic (EC) window devices, are well known for useas mirrors in motor vehicles, aircraft window assemblies, sunroofs,skylights, and architectural windows. Such devices may comprise, forexample, active inorganic electrochromic layers, organic electrochromiclayers, inorganic ion-conducting layers, organic ion conducting layersand hybrids of these sandwiched between two conducting layers. When avoltage is applied across these conducting layers the optical propertiesof a layer or layers in between change. Such optical property changestypically include a modulation of the transmissivity of the visibleportion or the solar sub-portion of the electromagnetic spectrum. Forconvenience, the two optical states will be referred to as a bleachedstate and a darkened state in the present disclosure, but it should beunderstood that these are merely examples and relative terms (i.e., afirst one of the two states is more transmissive or “more bleached” thanthe other state and the other of the two states is less transmissive or“more darkened” than the first state) and that there could be a set ofbleached and darkened states between the most transmissive state and theleast transmissive state that are attainable for a specificelectrochromic device; for example, it is feasible to switch betweenintermediate bleached and darkened states in such a set.

The broad adoption of electrochromic window devices in the constructionand automotive industries will require a ready supply of low cost,aesthetically appealing, durable products in large area formats.Electrochromic window devices based on metal oxides represent the mostpromising technology for these needs. Typically, such devices comprisetwo electrochromic materials (a cathode and an anode) separated by anion-conducting film and sandwiched between two transparent conductingoxide (TCO) layers. In operation, a voltage is applied across the devicethat causes current to flow in the external circuit, oxidation andreduction of the electrode materials and, to maintain charge balance,mobile cations to enter or leave the electrodes. This facileelectrochemical process causes the window to reversibly change from amore bleached (e.g., a relatively greater optical transmissivity) to amore darkened state (e.g., a relatively lesser optical transmissivity).

Electrochromic devices may utilize a combination of two types ofelectrochromic materials, one of which becomes optically lesstransmissive (e.g., takes on color) in its electrochemically oxidizedstate while the other becomes optically less transmissive (e.g., takeson color) in its electrochemically reduced state. Such a device whereboth anodic and cathodic electrochromic materials can simultaneouslydarken or bleach may be called a complementary electrochromic device.For example, Prussian blue assumes a blue color in its electrochemicallyoxidized state and becomes colorless by reduction while tungstentrioxide (i.e., WO₃), assumes a blue color in its electrochemicallyreduced state and becomes colorless by oxidation. When the two are usedas separate electrochromic layers separated by an ion conductor layer ina multi-layer stack, the stack may be reversibly cycled between a bluecolor (when the Prussian blue material is in its electrochemicallyoxidized state and tungsten trioxide is in its reduced state) and atransparent state (when the Prussian blue material is in itselectrochemically reduced state and tungsten trioxide is in itselectrochemically oxidized state) by application of an appropriatevoltage across the stack.

For convenience of description herein, change of these one or moreoptical properties of electrochromic devices (i.e., switching or cyclingof the electrochromic devices) is primarily discussed as occurringbetween a pair of optical states (i.e., an optically less transmissivestate and an optically more transmissive state), but it should beunderstood that these are merely examples and relative terms. Forexample, the optically less and more transmissive states can be a pairof optical states between a pair of more extreme optically less and moretransmissive states that are attainable by a specific electrochromicdevice. Further, there could be any number of optical states between theoptically less and more transmissive states.

Tungsten oxides are well-known electrochemically active materials.Uncertainty exists in the literature, however, regarding whethercrystalline or amorphous materials are preferred. In addition, whiletungsten trioxide (WO₃) crystallizes in several polymorphs, there is noclear preference as to which polymorph is best, or whether demonstrabledifferences should be expected. Crystallinity, the degree ofcrystallinity, and the crystal system obtained varies with synthesismethod, temperature, the use of additives and other considerations.

Some electrochromic systems in prior art literature have studiedamorphous WO₃ prepared by physical vapor deposition (PVD). Many examplesin the PVD literature teach that crystalline WO₃ is detrimental for ECperformance. Crystalline WO₃ in these studies tends to be deposited ontoa hot substrate, or crystallized from an amorphous deposition, and ismost often of monoclinic symmetry.

In addition to thermal evaporation, WO₃ can be deposited by a number ofother methods, such as sol-gel, electrodeposition and hydrothermalsynthesis. Different deposition methods can be used to prepare WO₃ filmswith different crystal structures. While not every polymorph may beprepared in a straightforward manner, methods for the synthesis of eachare known.

WO₃ may be prepared from sol-gel methods requiring expensive precursorsand organic solvents. These reagents contain significant amounts ofcarbon from their (often) alkoxide ligands and this carbon must beremoved later in the process, often using elevated temperatures. Inaddition, some WO₃ film deposition methods require the use of bindersand templating agents to facilitate the synthesis of differentpolymorphs of WO₃ and/or impart robust mechanical properties to thedeposited films. These binders and templating agents remain in the filmafter deposition diluting the active material in the film, and/orrequire complex processing conditions to remove.

The prior art has shown the deposition of crystalline WO₃ films thatrequire high temperature treatments of the films on the substrate. Onedeposition method is hot wire chemical vapor deposition to form WO₃nanoparticles followed by electrophoretic deposition of a film, andanother deposition method was thermal evaporation. Both techniques usedrequired a post-deposition anneal at 300-400° C. for 2 hours to form theintended crystalline films. These techniques requiring high temperaturepost-deposition annealing are not feasible for films formed onsubstrates that can be altered or melt at those temperatures.

Crystalline tungsten trioxide films can be deposited directly on asubstrate using techniques such as thermal evaporation or sol-gelmethods with annealing. Sol-gel methods require high temperatures afterdeposition to create crystalline tungsten trioxide films with the mostdesirable electrochromic properties. Crystalline hexagonal tungstentrioxide nanostructures (e.g. nanowires and/or nanoparticles) can begrown on tungsten trioxide seed layers as well. Physical vapor deposited(e.g., evaporated or sputtered) films are typically amorphousas-deposited unless the substrate is heated, and may also thus requirethermal treatments to crystallize the films after deposition. The hightemperatures required to crystallize an as-deposited amorphous filmproduced by physical vapor deposition to form crystalline tungstentrioxide are incompatible with substrates with low melting points (e.g.flexible polymer substrates). The high temperatures and environmentsrequired for post-deposition annealing also require more expensiveequipment. Additionally, some processing temperatures required for thecrystallization of certain tungsten trioxide polymorphs can reach ashigh as 900° C., which precludes the use of glass substrates if thematerial is deposited directly onto the substrate before thecrystallization step. These techniques all have drawbacks inmanufacturing compared to hydrothermal synthesis of crystalline tungstentrioxide particles, followed by size-reduction and coating, especiallywhen targeting crystalline particles of a specific symmetry orstructure.

One of the crystal phases of WO₃ that has been studied by certainprocessing techniques is hexagonal WO₃ (i.e., h-WO₃). There are someexamples of hexagonal WO₃ (i.e. h-WO₃) for battery (i.e.electrochemical) and EC applications in the prior art. Commonly utilizedsynthetic methods such as PVD and electrodeposition, however, are notalways amenable to the preparation of single phase, crystalline h-WO₃.Instead, h-WO₃ has been produced via hydrothermal synthesis, growingnanostructures directly on substrates, and producing nanostructures insolution.

Other crystal phases of WO₃ have other symmetries and may be describedas triclinic WO₃ or monoclinic WO₃ or cubic WO₃, as is appropriate basedon their symmetries. In general, if the arrangement of the atoms in thecrystal phase are similar but differ in symmetry, the crystal phase maybe described strictly by its symmetry. In certain circumstances,however, the arrangement of the atoms in the crystal phase may be uniquebeyond simple distortions that alter the lattice symmetry. In suchcases, the use of structure types in addition to a symmetry descriptoris useful

Tungsten oxide thus may be described as displaying a number ofpolymorphs. The term “polymorph” is here intended to comprise symmetrychanges that largely maintain some or all of the same atomicconnectivity and unique relationships of atoms that produce uniquestructural features. Sometimes, however, polymorph may describe anentirely different structure and atomic arrangement but with the samecomposition. Critically, the synthesis and/or thin film depositionmethod can impact the resulting polymorph. For instance, thermallyevaporated tungsten oxide is typically amorphous especially if thesubstrate is not heated. The resulting films can be crystallized bypost-deposition annealing (e.g., in air), however, the resulting crystalstructure of the tungsten trioxide so produced is typically monoclinicperovskite. Monoclinic perovskite tungsten oxide is known to undergophase transformations upon intercalation (e.g. with Li).[Nonstoichiometric Compounds; Ward, R.; Advances in Chemistry; Chapter23, pp 246-253, American Chemical Society: Washington, D C, 1963.]Examples of tungsten trioxide materials that typically occur indifferent structures are sol-gel prepared materials and commerciallyavailable nanostructured materials which typically have the “PerovskiteTungsten Bronze” [or PTB] structure. The PTB structure may be describedas similar to ReO₃ in which metal (M) ions (usually monovalent) areintercalated into interstitial spaces of the ReO₃ structure resulting inM_(x)ReO₃ and the perovskite structure type. Also, it is well known inthe literature that thermally evaporated films that have subsequentlybeen crystallized by annealing show worse durability than the amorphoustungsten trioxide thermally evaporated films in electrochromic devices.

Another polymorph of WO₃ is the cubic pyrochlore. Sometimes thestoichiometry is represented with waters of hydration and sometimes withhydroxides. Sometimes the stoichiometry is represented with counter ionsand sometimes the stoichiometry is doubled, e.g. [—]W₂O₆. Forsimplicity, the pyrochlore phase will be described here as part of theWO₃ series and explained as a substituted WO₃ when additional metals arepresent.

The film deposition approaches of many crystalline tungsten oxidepolymorphs have limitations. For example, h-WO₃ nanowires formed byhydrothermal synthesis directly on substrates required a 400° C.pretreatment step to form a WO₃ seed layer. This pretreatment step isnot compatible with many low temperature substrates. Additionally, thesefilms had poor mechanical properties, such as low adhesion to theunderlying substrate. Hexagonal-WO₃ nanostructures have also beenproduced in solution, but have either not been deposited into films(i.e. characterized as a colloidal dispersion only), or were depositedin a composite film using conductive carbon and binders (to addressimproving the mechanical properties, such as adhesion).

What is therefore desired are crystalline tungsten oxide electrochromicmaterials capable of forming films and devices on a variety ofsubstrates, and methods for producing the same. Furthermore, anelectrochromic device with crystalline tungsten oxide and methods forproducing the same, with improved device durability, is also desirable.It is within this context that the embodiments arise.

BRIEF DESCRIPTION OF THE DRAWINGS

To facilitate further description of the embodiments, the followingdrawings are provided in which:

FIG. 1 illustrates four different polymorphs of tungsten trioxide:monoclinic perovskite, tetragonal perovskite, hexagonal and pyrochloreincluding the approximate interstitial dimensions.

FIG. 2 is a schematic cross-section of a multi-layer electrochromicdevice of the present disclosure.

FIG. 3a illustrates an x-ray diffraction pattern for hexagonal tungstenoxide, produced by hydrothermal synthesis methods.

FIG. 3b illustrates an x-ray diffraction pattern for pyrochlore tungstenoxide, produced by hydrothermal synthesis methods.

FIG. 4a illustrates an x-ray diffraction pattern for a hexagonaltungsten oxide powder sample, produced by hydrothermal synthesismethods, and the same powder coated on an FTO coated glass substrateafter size-reduction.

FIG. 4b illustrates a particle size distribution of hexagonal tungstentrioxide slurries after size-reduction by grinding.

FIG. 5a illustrates an x-ray diffraction pattern for a pyrochloretungsten oxide powder sample, produced by hydrothermal synthesismethods, and the same powder coated on an ITO/TTO coated glass substrateafter size-reduction.

FIG. 5b illustrates a particle size distribution of pyrochlore tungstenoxide slurries after size-reduction by grinding.

FIG. 6a illustrates the % transmission vs. wavelength spectra of ahexagonal tungsten oxide film in the bleached and darkened states.

FIG. 6b illustrates the % transmission vs. wavelength spectra of apyrochlore tungsten oxide film in the bleached and darkened states.

FIG. 7a illustrates the % fade (percent change in capacity between cycle2 and cycle 23) for a perovskite WO₃ EC device compared to a hexagonalWO₃ EC device and a pyrochlore tungsten oxide EC device.

FIG. 7b illustrates the switching rate (reduction in capacity observedwhen the material is reduced at a current I equal to the initial Q(C)/120 s rather than at 25×10⁻⁶ Amp) for a perovskite WO₃ EC devicecompared to a hexagonal WO₃ EC device and a pyrochlore tungsten oxide ECdevice. Initial Q is the capacity obtained when switching at 25×10⁻⁶Amps between bleached and darkened states.

Corresponding reference characters indicate corresponding partsthroughout the drawings. Additionally, relative thicknesses of thelayers in the different figures do not represent the true relationshipin dimensions. For example in FIG. 2, the substrates are typically muchthicker than the other layers. Unless otherwise noted, the figures aredrawn only to illustrate connection principles, not to give anydimensional information.

ABBREVIATIONS AND DEFINITIONS

The following definitions are provided to better define the embodimentsof the present disclosure and to guide those of ordinary skill in theart in the practice of the present disclosure. Unless otherwise noted,terms are to be understood according to conventional usage by those ofordinary skill in the relevant art.

The terms “first,” “second,” “third,” “fourth,” and the like in thedescription and in the claims, if any, are used for distinguishingbetween similar elements and not necessarily for describing a particularsequential or chronological order. It is to be understood that the termsso used are interchangeable under appropriate circumstances such thatthe embodiments described herein are, for example, capable of operationin sequences other than those illustrated or otherwise described herein.Furthermore, the terms “include,” and “have,” and any variationsthereof, are intended to cover a non-exclusive inclusion, such that anactivity, process, method, system, article, device, or apparatus thatcomprises a list of elements is not necessarily limited to thoseelements, but may include other elements not expressly listed orinherent to such activity, process, method, system, article, device, orapparatus.

The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,”“under,” and the like in the description and in the claims, if any, areused for descriptive purposes and not necessarily for describingpermanent relative positions. It is to be understood that the terms soused are interchangeable under appropriate circumstances such that theembodiments of the disclosure described herein are, for example, capableof operation in other orientations than those illustrated or otherwisedescribed herein.

The terms “couple,” “coupled,” “couples,” “coupling,” and the likeshould be broadly understood and refer to connecting two or moreelements or signals, electrically, ionically, mechanically and/orotherwise. Two or more electrical elements may be electrically coupledbut not be mechanically or otherwise coupled; two or more mechanicalelements may be mechanically coupled, but not be electrically orotherwise coupled; two or more electrical elements may be mechanicallycoupled, but not be electrically or otherwise coupled. Coupling may befor any length of time (e.g., permanent or semi-permanent or only for aninstant).

“Electrical coupling” and the like should be broadly understood andinclude coupling involving any electrical signal, whether a powersignal, a data signal, and/or other types or combinations of electricalsignals.

“Ionic coupling” and the like should be broadly understood and includecoupling involving or permitting the transfer of ions between discretelayers or compositions.

“Mechanical coupling” and the like should be broadly understood andinclude mechanical coupling of all types.

The absence of the word “removably,” “removable,” and the like near theword “coupled,” and the like does not mean that the coupling, etc. inquestion is or is not removable.

The terms “anodic electrochromic layer” and “anodic electrochromicmaterial” refer to an electrode layer or electrode material,respectively, that upon the removal of ions and electrons becomes lesstransmissive to electromagnetic radiation.

The term “bleach” refers to the transition of an electrochromic materialfrom a first optical state to a second optical state wherein the firstoptical state is less transmissive than the second optical state.

The term “bleached state voltage” refers to the open circuit voltage(Voc) of the anodic electrochromic layer versus Li/Li+ in anelectrochemical cell in a propylene carbonate solution containing 1Mlithium perchlorate when the transmissivity of said layer is at 95% ofits “fully bleached state” transmissivity.

The terms “cathodic electrochromic layer” and “cathodic electrochromicmaterial” refer to an electrode layer or electrode material,respectively, that upon the insertion of ions and electrons becomes lesstransmissive to electromagnetic radiation.

The term “coloration efficiency” or “CE” refers to a property of anelectrochromic layer that quantifies how a layer's optical densitychanges as a function of its state of charge. CE can vary significantlydepending on layer preparation due to differences in structure, materialphases, and/or composition. These differences affect the probability ofelectronic transitions that are manifest as color. As such, CE is asensitive and quantitative descriptor of an electrochromic layerencompassing the ensemble of the identity of the redox centers, theirlocal environments, and their relative ratios. CE is calculated from theratio of the change in optical absorbance to the amount of chargedensity passed. In the absence of significant changes in reflectivity,this wavelength dependent property can be measured over a transition ofinterest using the following equation:

${CE}_{\lambda} = \frac{\log_{10}\left( \frac{T_{ini}}{T_{final}} \right)}{Q_{A}}$

where Q_(A) is the charge per area passed, T_(ini) is the initialtransmission, and T_(final) is the final transmission. For anodicallycoloring layers this value is negative, and may also be stated inabsolute (non-negative) values. A simple electro-optical setup thatsimultaneously measures transmission and charge can be used to measureCE. Alternatively, the end transmission states can be measured ex situbefore and after electrical switching. CE is sometimes alternativelyreported on a natural log basis, in which case the reported values areapproximately 2.3 times larger.

The term “darken” refers to the transition of an electrochromic materialfrom a first optical state to a second optical state wherein the firstoptical state is more transmissive than the second optical state.

The term “electrochromic material” refers to materials that change intransmissivity to electromagnetic radiation, reversibly, as a result ofthe insertion or extraction of ions and electrons. For example, anelectrochromic material may change between a colored, translucent stateand/or a transparent state.

The term “electrochromic layer” refers to a layer comprising anelectrochromic material.

The term “electrode layer” refers to a layer capable of conducting ionsas well as electrons. The electrode layer contains a species that can bereduced when ions are inserted into the material and contains a speciesthat can be oxidized when ions are extracted from the layer. This changein oxidation state of a species in the electrode layer is responsiblefor the change in optical properties in the device.

The term “electrical potential,” or simply “potential,” refers to thevoltage occurring across a device comprising an electrode/ionconductor/electrode assembly.

The term “electrochemically matched” refers to a set of cathode andanode electrochromic films or materials with similar charge capacitiesand complementary oxidation states such that when joined together by asuitable ion-conducting and electrically insulating layer, a functionalelectrochromic device is formed that shows reversible switching behaviorover a substantial range of the theoretical charge capacities of thefilms or materials, respectively.

The term “fully bleached state” as used in connection with an anodicelectrochromic material refers to the state of maximum transmissivity ofan anodic electrochromic layer in an electrochemical cell at or above1.5V versus Li/Li+ in a propylene carbonate solution containing 1 Mlithium perchlorate at 25° C. (under anhydrous conditions and in an Aratmosphere).

The term “inorganic electrochromic film” or “inorganic electrochromicmaterial” as used herein comprises a film or material, respectively,comprising metals that undergo reversible oxidation and reductionreactions during the cycling of an electrochromic device. Inorganicelectrochromic materials and films lack solubility in common organic andneutral aqueous solvents, and typically possess a 3-dimensionalstructure where the metal ions are bridged to and share counter anionssuch as oxide, sulfide, nitride and halide, or complex molecularinorganic anions such as silicate, borate, phosphate or sulfate.Electrochromic films comprising metal ions and carbon-containing counteranions in a 3-dimensional lattice are also known. Examples includePrussian blue and Prussian blue analogues, nitroprusside compounds andother metal-organic framework compounds comprising metal ions andcyanide anions or other anions similar to cyanide. These systems mayalso be referred to as organometallic electrochromic materials.

The term “transmissivity” refers to the fraction of light transmittedthrough an electrochromic film. Unless otherwise stated, thetransmissivity of an electrochromic film is represented by the numberT_(vis). T_(vis) is calculated/obtained by integrating the transmissionspectrum in the wavelength range of 400-730 nm using the spectralphotopic efficiency l_p (lambda) (CIE, 1924) as a weighting factor.(Ref: ASTM E1423).

The term “transparent” is used to denote substantial transmission ofelectromagnetic radiation through a material such that, for example,bodies situated beyond or behind the material can be distinctly seen orimaged using appropriate image sensing technology.

The term “nanostructure” or “nanostructures” as used herein refers tonanowires, nanoparticles, nanofoams, nanoporous films, or any structurewith dimensions between microscopic and molecular scale structures.

The term “grinding” as used herein refers to size-reduction of particlesby mechanical means. Some examples of grinding apparatuses are a mortarand pestle, various types of ball mills (e.g., planetary ball mill,agitator ball mill, etc.), various types of mills not using balls as themilling media (e.g., rod mill, vibrating mill, etc.), machines using anabrasive wheel as the cutting tool (e.g., a belt grinder or a benchgrinder), or other methods using mechanical force to size-reduceparticles. Additionally, size-reducing particles can refer to reducingthe size of the primary particles, or reducing the size of hard or softagglomerates comprising primary particles.

The term “hexagonal tungsten trioxide” as used herein refers to amaterial with the formula A_(y)W_(1−x)M_(x)O_(3±z).kH₂O), where A issituated within the hexagonal or hexagonal-like channels depicted inFIG. 1 and where M is substituted within the W—O lattice. As such, A isoften a monovalent species such as a proton, an ammonium ion, and/or analkali metal and may sometimes be an alkaline earth metal. M is atransition metal, other metal, lanthanide, actinide, electrochromicmetal or non-electrochromic metal in octahedral coordination. As such, xis from about 0 to about 1, y is from about 0 to about 0.5, and where zcan be from about −0.5 to about 0.5. The crystal structure may behexagonal or have hexagonal-like channels (for example, as depicted inthe hexagonal WO₃ structure in FIG. 1). The W(M)-O layers are stacked inthe [001] direction resulting in 1-dimensional channels. A and/or M alsocomprise more than one element and be expressed as A′_(a)+A″_(b)+A′″_(c)and/or M′_(d)+M″e+M′″_(f) where A′, A″ and A′″ and/or M′, M″ and M′″ aredifferent elements, where a+b+c=y and d+e+f=x. “Hexagonal tungstentrioxide” can refer to materials including atoms other than tungsten andoxygen, including but not limited to, substituted hexagonal tungstenoxide, hexagonal tungsten bronze and hexagonal tungsten bronze-likematerials. The term “hexagonal tungsten oxide” as used herein refers to“hexagonal tungsten trioxide” as defined above.

The term “pyrochlore” as used herein refers to a material with theformula A_(y)W_(1−x)M_(x)O_(3±z).kH₂O), where A is situated within thehexagonal or hexagonal-like channels depicted in FIG. 1 and where M issubstituted within the W—O lattice. As such, A is often a monovalentspecies such as a proton, an ammonium ion, and/or an alkali metal andmay sometimes be an alkaline earth metal. M is a transition metal, othermetal, lanthanide, actinide, electrochromic metal or non-electrochromicmetal in octahedral coordination. Under these conditions, x is fromabout 0 to about 1, y is from above 0 to about 0.5, and where z can befrom about −0.5 to about 0.5. The crystal structure may be hexagonal orhave hexagonal-like channels (for example, as depicted in the pyrochloreWO₃ structure in FIG. 1). Unlike in the hexagonal WO₃ structure, the W—Olayers are stacked in the [111] direction forming an interconnectednetwork of 3-dimensional channels. A and/or M also comprise more thanone element and be expressed as A′_(a)+A″_(b)+A′″_(c) and/orM′_(d)+M″_(e)+M′″_(f) where A′, A″ and A′″ and/or M′, M″ and M′″ aredifferent elements, where a+b+c=y and d+e+f=x. “Pyrochlore” can refer tomaterials comprising atoms other than tungsten and oxygen, including butnot limited to, pyrochlore-like, defected pyrochlore, defectedpyrochlore-like, substituted pyrochlore, substituted pyrochlore-like,and substituted, defected pyrochlore-like materials.

The term “tungsten trioxide” as used herein refers to a material withthe formula A_(y)W_(1−x)M_(x)O_(3±z).kH₂O) and has any crystal structurewhere A is situated within interstitial spaces and where M issubstituted within the W—O lattice. As such, A is often a monovalentspecies such as a proton, an ammonium ion, and/or an alkali metal andmay sometimes be an alkaline earth metal. M is a transition metal, othermetal, lanthanide, actinide, electrochromic metal or non-electrochromicmetal in octahedral coordination. Under these conditions, x is fromabout 0 to about 1, y is from above 0 to about 0.5, and where z can befrom about −0.5 to about 0.5. A and/or M also comprise more than oneelement and be expressed as A′_(a)+A″_(b)+A′″_(c) and/orM′_(d)+M″_(e)+M′″_(f) where A′, A″ and A′″ and/or M′, M″ and M′″ aredifferent elements, where a+b+c=y and d+e+f=x. “Tungsten trioxide” canrefer to materials comprising atoms other than tungsten and oxygen,including but not limited to, substituted tungsten oxide, substitutedtriclinic tungsten oxide, substituted monoclinic tungsten oxide,substituted orthorhombic tungsten oxide, substituted tetragonal tungstenoxide, substituted hexagonal tungsten oxide, or substituted cubictungsten oxide. Furthermore, “tungsten trioxide” can refer to structurescomprising hexagonal tungsten bronze, hexagonal tungsten bronze-likematerials, tetragonal tungsten bronze, tetragonal tungsten bronze-likematerials, pyrochlore materials, pyrochlore-like materials, defectedpyrochlore materials, defected pyrochlore-like materials, substitutedpyrochlore materials or substituted pyrochlore-like materials.

DETAILED DESCRIPTION

Embodiments of the current invention describe methods of producingdurable tungsten trioxide, hexagonal tungsten trioxide, or pyrochloreelectrochromic films using methods that are amenable to high volume, lowcost manufacturing. Additionally, embodiments of the current inventionalso describe films having robust mechanical properties and depositionmethods that are compatible with substrates requiring low maximumprocessing temperatures.

In particular, this disclosure describes a method to produce metal oxideparticles which are deposited as thin films with electrochromicproperties. In some embodiments, these particles are prepared usinghydrothermal synthesis. In some embodiments, these films are alsoincorporated into multi-layer stacks, and electrochromic devices. Insome cases these particles are tungsten trioxide, hexagonal tungstentrioxide, or pyrochlore particles.

Although there are particular embodiments describes of the tungstentrioxide, hexagonal tungsten trioxide, and pyrochlore variations of theinvention, these are not meant to be limiting. The term “polymorph” ishere intended to comprise symmetry changes that largely maintain some orall of the same atomic connectivity and unique relationships of atomsthat produce unique structural features. Sometimes, however, polymorphmay describe an entirely different structure and atomic arrangement butwith the same composition. The synthesis and/or thin film depositionmethod can impact the resulting polymorph. Additional polymorphs of thematerials include: triclinic tungsten oxide nanostructures, monoclinictungsten oxide nanostructures, orthorhombic tungsten oxidenanostructures, tetragonal tungsten oxide nanostructures, hexagonaltungsten oxide nanostructures, cubic tungsten oxide nanostructures,triclinic tungsten trioxide nanostructures, monoclinic tungsten trioxidenanostructures, orthorhombic tungsten trioxide nanostructures, hexagonaltungsten trioxide nanostructures, cubic tungsten oxide nanostructures,substituted triclinic tungsten trioxide nanostructures, substitutedmonoclinic tungsten trioxide nanostructures, substituted orthorhombictungsten trioxide nanostructures, substituted tetragonal tungstentrioxide nanostructures, substituted hexagonal tungsten trioxidenanostructures, substituted cubic tungsten oxide nanostructures.

This disclosure describes a method to produce a crystalline thin film,wherein crystalline particles are synthesized, size-reduced by grinding,formulated into an ink, and coated on a substrate to produce acrystalline thin film. The crystalline thin film may be anelectrochromic thin film where formed of an electrochromically activemetal oxide. This disclosure also describes an electrochromicmulti-layer stack comprising a thin film comprising crystallinenanostructures or crystalline metal oxide nanostructures, anelectrically conductive layer, and an outer substrate. These multi-layerstacks can also be incorporated into electrochromic devices, such asautomobile mirrors and architectural windows. In another embodiment thecrystalline thin film has no extra material added such as a binder toenhance physical film characteristics. In some cases, thesenanostructures are tungsten trioxide, hexagonal tungsten trioxide, orpyrochlore nanostructures.

This disclosure also describes a method to produce a crystalline thinfilm, where the substrate may be stable under high temperatureconditions, for example glass or quartz or where the substrate may beunstable under high temperature conditions, for example plastics (e.g.polycarbonates, polyacrylics, polyurethanes, urethane carbonatecopolymers, polysulfones, polyimides, polyacrylates, polyethers,polyester, polyethylenes, polyalkenes, polyimides, polysulfides,polyvinylacetates and cellulose-based polymers). In an embodiment, thecrystalline particles used in the crystalline thin film may comprise atransition metal oxide or a main group metal oxide The crystalline thinfilm may also be formed of a mixed metal oxide comprising alkali metals,alkaline earth metals, transition metals, main group metals andlanthanide metals or a mixed metal oxide comprising metals andnon-metals where the non-metals are may be part of a complex anion suchas phosphate, sulfate, selenate, tellurate, silicate, germanate orcarbonate. The method to produce the crystalline electrochromic metaloxide thin film may include the synthesizing of the crystallineelectrochromic metal oxide particles, the size-reducing of thoseparticles by grinding, the formulating of the size-reduced particlesinto an ink, and coating the ink on a substrate to produce a crystallineelectrochromic metal oxide thin film. In some cases these particles aretungsten trioxide, hexagonal tungsten trioxide, or pyrochlore particles.

In a more particular embodiment, this disclosure describes methods toproduce a thin film of crystalline tungsten oxide, crystalline tungstentrioxide with hexagonal channels, or a crystalline pyrochlore. Thecrystalline tungsten oxide, hexagonal tungsten trioxide, or pyrochlorethin film may be a nanostructure. The crystalline tungsten trioxide orhexagonal tungsten trioxide or pyrochlore may be part of anelectrochromic multi-layer stack which also includes an electricallyconductive layer and an outer substrate. These multi-layer stacks canalso be incorporated into electrochromic devices, such as automobilemirrors and architectural windows.

In some embodiments, the crystalline tungsten oxide particles orcrystalline tungsten trioxide particles, or crystalline hexagonaltungsten trioxide particles or crystalline pyrochlore particles areproduced using hydrothermal synthesis. The hydrothermal synthesisprocess provides crystalline material in a mixture with a liquid, which,after further size reduction, can be coated on a substrate. In someembodiments, the crystalline tungsten oxide particles or crystallinetungsten trioxide particles, or crystalline hexagonal tungsten trioxideparticles, or crystalline pyrochlore particles are produced using sealedtube synthesis, solid state synthesis, or any synthetic method that canbe demonstrated by XRD to prepare crystalline tungsten oxide,crystalline tungsten trioxide, crystalline hexagonal tungsten trioxideor crystalline pyrochlore.

There are a number of advantages of this approach to create acrystalline tungsten oxide, or tungsten trioxide, or pyrochlore thinfilm on a substrate, such as eliminating the exposure of the substrateto high temperatures, and reducing the equipment and materials costscompared to other state of the art methods such as hydrothermalsynthesis directly on a substrate, sol-gel followed by annealing, andphysical vapor deposition followed by annealing.

Certain literature teaches away from the use of crystalline materialsfor electrochromic applications sometimes for synthetic considerations,sometimes for durability considerations, sometimes for rateconsiderations and sometimes for coloration efficiency considerations.Regarding synthetic considerations, often solid state transition metaloxides require fairly high temperatures for crystallization. The needfor high temperatures has implicitly taught away from crystallinitybecause of the inability of even glass substrates to tolerate thetemperatures commonly required. The methodology described here enablesthe use of any synthetic method and any temperature that may benecessary because synthesis is removed entirely from the substrate bybeing performed in advance of the deposition of the material on thesubstrate. Furthermore, the method also allows for a significantlylarger opportunity for purification and characterization of the activespecies since the material is prepared entirely before deposition to thesubstrate. Regarding the durability, rate and coloration efficiencyconsiderations, crystalline tungsten trioxide electrochromic behaviorcan vary widely depending on the polymorph of tungsten trioxide in thedevice. There are some polymorphs of tungsten trioxide, namely hexagonaltungsten trioxide and pyrochlore, which exhibit durability, rates andcoloration efficiency in electrochromic devices that is much improvedover the typical crystalline tungsten trioxide phases in the literature(e.g., perovskite tungsten trioxide). Not being held to any particulartheory, the fact that hexagonal tungsten trioxide and pyrochlore arestructurally stable upon insertion and de-insertion of lithium, sodiumand other ions is believed to be beneficial.

Tungsten Oxide Nanostructure Thin Films with Large Channels

This disclosure describes a method of producing or manufacturing a thinfilm including: providing a plurality of crystalline tungsten oxideparticles, size-reducing the crystalline tungsten oxide particles bygrinding to produce crystalline tungsten oxide nanostructures,formulating an ink of the size-reduced crystalline tungsten oxidenanostructures, and coating the ink onto a substrate to produce a thinfilm. This disclosure also describes an electrochromic multi-layer stackcomprising a thin film comprising crystalline tungsten oxidenanostructures, an electrically conductive layer, and an outersubstrate. This disclosure also describes the multi-layer stackincorporated into an electrochromic device. The tungsten oxide particlesmay be tungsten trioxide, or hexagonal tungsten trioxide, or pyrochlore.

In some embodiments, the tungsten oxide nanostructures comprisecrystalline hexagonal tungsten trioxide, or crystalline pyrochlore. Oneadvantage identified by the preparation of films using embodiments ofthe methodologies disclosed herein is that hexagonal tungsten trioxideand pyrochlore do not experience a phase change upon intercalation withLi. Not to be limited by theory, the hexagonal tungsten trioxide andpyrochlore crystal structures have large open channels throughout,(FIG. 1) that are hypothesized to aid in the diffusion of Li and canaccommodate the Li ions without detrimental lattice strain and phasechanges associated with poor electrochromic durability. It is thereforedesirable to produce thin films containing large open channels, such ashexagonal tungsten trioxide or pyrochlore thin films, for use aselectrochromic active layers in electrochromic multi-layer stacks anddevices.

Hexagonal tungsten trioxide can have a crystal structure of the spacegroup P6/mmm (#191), where the lattice parameters are a=b=approximately7.3 (Angstroms), and c=approximately 3.9 (Angstroms). The c-axis canalso be reported as two times the 3.9 Å c-axis, in other wordsapproximately 7.8 Å. In some instances, small compositional changes mayresult in a change of crystal symmetry. In such cases, a substitutedhexagonal tungsten trioxide may have lower than hexagonal symmetry andmay not crystallize in space group P6/mmm. The arrangement of atoms maybe largely the same, however, and arranged as described herein and asshown in FIG. 1. In some embodiments, the structure of hexagonaltungsten trioxide can be described as layers of corner sharing WO₆octahedra perpendicular to the c-axis with 3- and 6-sided cavities inthe a-b plane. If the space group is in fact P6/mmm, or anotherhexagonal group, the cavities may have 3- and 6-fold rotationalsymmetry. If the space group is of lower symmetry, the arrangement ofatoms results in cavities that may have the appearance of 3- and 6-foldrotational symmetry without actually possessing this symmetry.

In some embodiments, the structure of pyrochlore tungsten trioxide canbe described as tetrahedral clusters of corner sharing WO₆ octahedra.These clusters are connected to form a kagome net. From anotherperspective, the structure can be described as corner sharing WO₆octahedra 6-sided cavities which are not parallel to each other, butinstead form larger tetrahedron structures where the 6-sided cavitiesare centered on the faces of the tetrahedrons. The pyrochlore structurecontains structural components which are similar to the hexagonalstructure (the 3- and 6-sided cavities), but in the case of thepyrochlore structure these components are arranged in 3-dimensionsinstead of layers. If the space group is of a cubic symmetry with spacegroup Fd-3m, then the described elements will also possess rotationalsymmetry elements. If the structure is distorted to another crystalsystem, then these symmetry elements may be broken, but the generalconnectivity of the WO₆ octahedra will remain intact.

Hexagonal tungsten trioxide and pyrochlore compounds are distinct fromother more common tungsten oxide materials which have different crystalstructures and different symmetries. FIG. 1 illustrates four differentpolymorphs of tungsten trioxide: monoclinic perovskite, tetragonalperovskite, hexagonal and pyrochlore. The dimensions of the largestinterstitial sites are also shown. The channels throughout the hexagonaltungsten trioxide and pyrochlore structures are the largest, withcharacteristic dimensions of 5.36×5.36 Angstroms and 5.34×5.34Angstroms, respectively. Monoclinic perovskite and tetragonal perovskitetungsten trioxide have interstitial sites that are smaller and in somecases asymmetric, with dimensions from 3.08 to 4.47 Angstroms, as shownin FIG. 1. Not to be limited by theory, in a material in which ions areto be repetitively intercalated and deintercalated, it is desirable tohave an interstitial site that is sufficiently large to enable ionmobility. Further, it is desirable to have an interstitial site that issufficiently large such that repetitive ion removal and insertion doesnot result in significant lattice strain, furthermore, it is desirableto have a crystal structure that can tolerate repetitive ion removal andinsertion without undergoing a structural phase transition.

As defined above, “hexagonal tungsten trioxide” or “pyrochlore,” as usedherein has the formula A_(y)W_(−1-x)M_(x)O_(3±z).kH₂O), where A issituated within the hexagonal or hexagonal-like channels depicted inFIG. 1 and where M is substituted within the W—O lattice. A is often amonovalent species such as a proton, an ammonium ion, and/or an alkalimetal and may sometimes be an alkaline earth metal. M is a transitionmetal, other metal, lanthanide, actinide, electrochromic metal ornon-electrochromic metal in octahedral coordination. As such, x is fromabout 0 to about 1, y is from about 0 to about 0.5, and where z can befrom about −0.5 to about 0.5. The crystal structure may be hexagonal orhexagonal-like channels (for example, as depicted in both the hexagonalWO₃ structure and the pyrochlore structure in FIG. 1). A and/or M alsocomprise more than one element and be expressed as A′_(a)+A″_(b)+A′″_(c)and/or M′_(d)+M″_(e)+M′″_(f) where A′, A″ and A′″ and/or M′, M″ and M′″are different elements, where a+b+c=y and d+e+f=x. It follows that“hexagonal tungsten trioxide” or “pyrochlore” can refer to materialsincluding atoms other than tungsten and oxygen, including but notlimited to, substituted hexagonal tungsten oxide, hexagonal tungstenbronze and hexagonal tungsten bronze-like materials or pyrochlore-like,defected pyrochlore, defected pyrochlore-like, substituted pyrochlore,substituted pyrochlore-like, and substituted, defected pyrochlore-likematerials, respectively. The term “hexagonal tungsten oxide” as usedherein refers to “hexagonal tungsten trioxide” as defined above whilethe term “pyrochlore” as used herein refers to pyrochlore, pyrochloreWO₃, p-WO₃ or py-WO₃ as defined above. In some embodiments, tungstentrioxide or hexagonal tungsten trioxide or pyrochlore has a compositiondescribed by the formula WO_(3−x), where x describes a small number ofoxygen vacancies. In some embodiments x has a value from 0 to 0.05, orfrom 0.05 to 0.1, or from 0 to 0.1, or from 0.1 to 0.2. If the tungstentrioxide compound has too little oxygen, often it will have lowtransmission in the oxidized state. For example, a ratio of tungsten tooxygen that is less than 1:3 implies that the oxidation state of thetungsten is less than 6⁺. In such a situation, the material could beexpected to demonstrate low transmission. Low transmission in thebleached state is undesirable in certain applications, such as for filmsthat are used as cathodes in electrochromic devices. In someembodiments, tungsten can be augmented by the addition of substitutedmetals that have an oxidation state less than 6+. In certain cases, thematerial may display a metal (tungsten+substituted metal) to oxygenratio that is less than 1:3 if all metals are in their highest oxidationstate. In these cases, a ratio that is less than 1:3 may not result inlow transmission. In some embodiments, tungsten can be replaced by othermetals and still maintain the hexagonal tungsten oxide structure orpyrochlore structure shown in FIG. 1. As defined herein, hexagonaltungsten oxide or pyrochlore comprises tungsten, oxygen and othercations or anions such that the hexagonal tungsten oxide or pyrochloreatomic arrangement is maintained, in a general sense, respectively. Forexample, tungsten may be partially substituted by molybdenum or anothermetal. If the partial substitution results in crystallographic ordering,the lattice parameters may change and/or the space group, crystalsymmetry and atomic positions may change but the general arrangement ofatoms in 3 dimensions is maintained. In some embodiments, M can be amobile cation that can be intercalated/deintercalated. These mobilecations are largely +1 cations but could be +2 cations also (e.g. Li⁺,Na⁺, K⁺, Rb⁺, Cs⁺, NH4⁺, H⁺, Mg²⁺, Ca²⁺). In some embodiments, M can beEC active metals including early transition metals or main group metalsthat are octahedrally coordinated, in which the highest oxidation statesare clear or lightly colored, and are redox active in the voltage rangeof interest (e.g. V, Nb, Ta, Cr, Mo, Ti, Sb, Sn). In some embodiments, Mcan be an EC inactive metal including early transition metals or maingroup metals that are octahedrally coordinated, in which stableoxidation states are clear or lightly colored, and are not redox activein the voltage range of interest (e.g. Hf, In, Ga, Ge).

In some embodiments, the crystalline hexagonal tungsten trioxide orpyrochlore nanostructures are nano-scale in 3 dimensions (i.e. arenanoparticles, not nanowires).

In some embodiments, the crystalline hexagonal tungsten trioxide orpyrochlore particles are produced via hydrothermal synthesis. In someembodiments, the crystalline hexagonal tungsten trioxide or pyrochloreparticles are produced by hydrothermal synthesis, then size-reduced bygrinding to produce crystalline hexagonal tungsten trioxide orpyrochlore nanostructures, then the nanostructures are formulated intoan ink, then the ink is coated onto a substrate. In an embodiment, theink is made without the addition of a binder which simplifies theformulation of the material and improves the manufacturability ofelectrochromic films deposited using methods described herein.

The substrate onto which the above films may be deposited may have amelting point less than 1000° C., or less than 900° C., less than 800°C., or less than 700° C., or less than 600° C., or less than 500° C., orless than 400° C., or less than 300° C., or less than 250° C., or lessthan 200° C., or less than 150° C., or less than 100° C., or from 100°C. to 200° C., or from 200° C. to 300° C., or from 300° C. to 400° C.,or from 400° C. to 500° C., or from 500° C. to 600° C., or from 600° C.to 700° C., or from 700° C. to 800° C., or from 800° C. to 900° C., orfrom 900° C. to 1000° C., or from 1000° C. to 1100° C., or from 1100° C.to 1200° C., or from 1200° C. to 1300° C., or from 1300° C. to 1400° C.,or from 1400° C. to 1500° C., or from 1500° C. to 1600° C.

In one embodiment of the current invention, the substrate may be thickerthan 50 micron. The substrate may also be an electrically conductinglayer and an outer substrate, where the material of the outer substratemay be selected from materials such as glass (e.g. soda lime glass orborosilicate glass), and plastic (e.g. polycarbonates, polyacrylics,polyurethanes, urethane carbonate copolymers, polysulfones, polyimides,polyacrylates, polyethers, polyester, polyethylenes, polyalkenes,polyimides, polysulfides, polyvinylacetates and cellulose-basedpolymers). The material of the electrically conductive layer may beselected from a group consisting of: transparent conductive oxides, thinmetallic coatings, networks of conductive nanoparticles (e.g., rods,tubes, dots), conductive metal nitrides, and composite conductors.

In some embodiments the reagents for the hydrothermal synthesis of thehexagonal tungsten trioxide or pyrochlore are Na₂WO₄*2H₂O, NaCl, DI H₂Oand HCl. In some embodiments the ratio by mass of Na₂WO₄*2H₂O to NaCl is4:1, or is 5:1, or is 6:1, or is 7:1, or is 10:1, or is 5:2, or is 5:3,or is 5:4, or is 1:1, or is 5:6, or is 5:7, or is 1:2. In someembodiments the ratio by mass of Na₂WO₄*2H₂O plus NaCl to DI H₂O is2:45, or is 4:45, or is 6:45, or is 8:45, or is 10:45, or is 15:45, oris 20:45.

In some embodiments, the reagents for the hydrothermal synthesis of thehexagonal tungsten trioxide or pyrochlore could comprise Li₂WO₄, Na₂WO₄,K₂WO₄, Rb₂WO₄, Cs₂WO₄ or H₂WO₄, in addition to or instead of Na₂WO₄*2H₂Oin the above set of reagents. Additionally, these alkali reagents couldbe produced in situ during the reaction to form hexagonal tungstentrioxide or pyrochlore, for instance by adding H₂O₂ to tungsten metal.

In some embodiments, the reagents for the hydrothermal synthesis of thehexagonal tungsten trioxide or pyrochlore could comprise Na₂SO₄, citricacid, aniline, ammonium tartrate, tartartic acid, other alkali sulfates(e.g., Li₂SO₄), or other alkali chlorides (e.g., LiCl), in addition toor instead of NaCl in the above set of reagents. The preceding list isnot limiting and other reagents and/or combinations of reagents will beobvious to those skilled in the art.

In some embodiments the pH of the hydrothermal synthesis of thehexagonal tungsten trioxide or pyrochlore reaction at the onset is 1.0,or is 1.5, or is 2, or is 2.5, or is 3, or is 3.5 or is 4.0, or is from1.0 to 2.5, or is from 1.9 to 2.1, or is from 1.5 to 2, or is from 2 to2.5 or is from 3.5 to 4.0. The pH has a large effect on the resultingphase of tungsten oxide created. For example, if the pH of thehydrothermal synthesis of the tungsten oxide reaction at the onset isless than 1.0, then a mixed phase tungsten oxide can be produced. Forexample, if the pH of the hydrothermal synthesis of the tungsten oxidereaction at the onset is 1.5, then hexagonal tungsten trioxide will beproduced. For example, if the pH of the hydrothermal synthesis of thetungsten oxide reaction at the onset is 3.5, then a hydrate pyrochlorestructure is produced.

In some embodiments, the hydrothermal synthesis of the hexagonaltungsten trioxide or pyrochlore reaction is held at 160° C. for 1 hour,or at 180° C. for 1 hour, or at 200° C. for 1 hour, or at 160° C. for 3hours, or at 180° C. for 3 hours, or at 200° C. for 3 hours, or at 160°C. for 4 hours, or at 180° C. for 4 hours, or at 200° C. for 4 hours, orat 160° C. for 5 hours, or at 180° C. for 5 hours, or at 200° C. for 5hours, or at 160° C. for 10 hours, or at 180° C. for 10 hours, or at200° C. for 10 hours, or at 160° C. for 12 hours, or at 180° C. for 12hours, or at 200° C. for 12 hours, or at 160° C. for 24 hours, or at180° C. for 24 hours, or at 200° C. for 24 hours, or at 160° C. for 48hours, or at 180° C. for 48 hours, or at 200° C. for 48 hours, or at160° C. for longer than 48 hours, or at 180° C. for longer than 48hours, or at 200° C. for longer than 48 hours.

In some embodiments the hydrothermally synthesized hexagonal tungstentrioxide or pyrochlore is washed on a filter. In some embodiments thehydrothermally synthesized hexagonal tungsten trioxide or pyrochlore iswashed using a centrifuge washing method. In some embodiments, DI wateris used to wash the hydrothermally synthesized tungsten trioxide. Insome embodiments, DI water followed by isopropyl alcohol is used to washthe hydrothermally synthesized tungsten trioxide. In other embodiments,any solvent in which the additive reagents are soluble followed by watercan be used in the washing process, such as 1 M LiOH followed by DIwater.

In some embodiments, the hydrothermally synthesized hexagonal tungstentrioxide or pyrochlore is washed, and separated from the washedcontaminants by centrifuging at 3000 rpm, or at 3500 rpm, or at 4000rpm, or at 4500 rpm, or at 5000 rpm, or at 5500 rpm, or at 6000 rpm. Insome embodiments, the hydrothermally synthesized tungsten oxide iswashed, and separated from the washed contaminants by washing andcentrifuging once, or by washing and centrifuging twice, by washing andcentrifuging three times, by washing and centrifuging four times, bywashing and centrifuging five times, by washing and centrifuging sixtimes, by washing and centrifuging using a continuous flow centrifugeprocess. In some embodiments, the washed contaminants could be removedfrom the hydrothermally synthesized tungsten oxide using a membranefiltering method.

In some embodiments, the hydrothermally synthesized hexagonal tungstentrioxide or pyrochlore could be further size-reduced by grinding. Insome embodiments the hydrothermally synthesized hexagonal tungstentrioxide or pyrochlore could be size-reduced using a mortar and pestle,or using an agitator bead mill, or using a planetary mill, or using alinear impact mill, or any method which reduces particle size throughmechanical means.

In some embodiments an agitator bead mill, or a planetary mill is usedto reduce the size of the hydrothermally synthesized hexagonal tungstentrioxide or pyrochlore, using milling media that is 0.03 mm in diameter,or 0.05 mm in diameter, or 0.1 mm in diameter, or 0.2 mm in diameter, or0.3 mm in diameter, or 0.4 mm in diameter, or 0.5 mm in diameter. Insome embodiments an agitator bead mill, or a planetary mill is used toreduce the size of the hydrothermally synthesized hexagonal tungstentrioxide or pyrochlore, using milling media that comprises a hardceramic material, or ZrO₂, or HfO₂, or Y₂O₃, or an alloy of ZrO₂ andHfO₂, or an alloy of ZrO₂ and Y₂O₃, or an alloy of ZrO₂ and HfO₂ andY₂O₃, or CeO₂, or an alloy of ZrO₂ and CeO₂, or SiO₂, or an alloy ofZrO₂ and SiO₂, or steel.

In some embodiments an agitator bead mill, or a planetary mill is usedto reduce the size of the hydrothermally synthesized hexagonal tungstentrioxide or pyrochlore, using water, isopropyl alcohol (IPA), propyleneglycol propyl ether (PGPE), or heptanol as the solvent. In someembodiments, low molecular weight alcohols (e.g., propanol or butanol),or organic solvents with viscosity less than 5 cP are used as a solvent.In some embodiments an agitator bead mill, or a planetary mill is usedto reduce the size of the hydrothermally synthesized hexagonal tungstentrioxide or pyrochlore, using multiple milling cycles, wherein eachcycle has an active milling period and an inactive period wherein themill is allowed to cool. In some embodiments an agitator bead mill, or aplanetary mill is used to reduce the size of the hydrothermallysynthesized tungsten oxide, using a milling speed of 500 rpm. In someembodiments an agitator bead mill, or a planetary mill is used to reducethe size of the hydrothermally synthesized tungsten oxide, wherein theactive milling period has a duration of from 1 to 10 min, and aninactive duration of from 1 to 10 min, and a total of from 5 to 50cycles. In some embodiments an agitator bead mill, or a planetary millis used to reduce the size of the hydrothermally synthesized tungstenoxide, wherein the mill is cooled and milling is performed for aduration of 10 min to 10 hours. In some embodiments an agitator beadmill, or a planetary mill is used to reduce the size of thehydrothermally synthesized tungsten oxide, wherein the milling isperformed until the particle size is less than 250 nm diameter, or lessthan 200 nm diameter, or less than 150 nm diameter, or less than 100 nmdiameter.

In some embodiments, milling is performed in a continuous manner. Insome embodiments, milling is performed in a continuous manner withfractions of the total milling volume. In some embodiments, milling isperformed in a continuous manner with fractions of the total millingvolume where the remainder of the total milling volume is stored in astorage vessel allowing cooling. In some embodiments, milling isperformed in a continuous manner such that the active milling period andthe inactive milling period are the same as milling performed in a batchmanner. In some embodiments, milling is performed using a mill withcontinuous circulation of the slurry from a holding tank to the millingchamber and/or a cooled milling chamber, which optionally enablesmilling processes without cooling periods.

In some embodiments, there is a first grinding step and a secondgrinding step using different methods to reduce the size of thehydrothermally synthesized hexagonal tungsten trioxide or pyrochlore. Insome embodiments, the first grinding step to reduce the size of thehydrothermally synthesized tungsten oxide comprises a mortar and pestle,and the second grinding step to reduce the size of the hydrothermallysynthesized tungsten oxide comprises an agitator bead mill, or aplanetary mill. In some embodiments the first grinding step comprises anagitator bead mill, or a planetary mill with a larger media size and thesecond grinding step comprises an agitator bead mill, or a planetarymill with a smaller media size.

In some embodiments the mean particle size of the size-reduced hexagonaltungsten trioxide or pyrochlore nanostructures after grinding is from 50to 300 nm, or from 100 to 300 nm, or from 150 to 300 nm, or from 200 to300 nm, or from 250 to 300 nm, or from 100 to 250 nm, or from 50 to 250nm, or from 50 to 200 nm, or from 50 to 150 nm, or from 50 to 100, orless than 300 nm, or less than 250 nm, or less than 200 nm, or less than150 nm, or less than 100 nm. In some embodiments the median particlesize of the size-reduced hexagonal tungsten trioxide or pyrochlorenanostructures after grinding is from 50 to 300 nm, or from 100 to 300nm, or from 150 to 300 nm, or from 200 to 300 nm, or from 250 to 300 nm,or from 100 to 250 nm, or from 50 to 250 nm, or from 50 to 200 nm, orfrom 50 to 150 nm, or from 50 to 100, or less than 300 nm, or less than250 nm, or less than 200 nm, or less than 150 nm, or less than 100 nm.

In some embodiments the polydispersity index (as defined in the ISOstandard document 13321:1996 E and ISO 22412:2008) of the particle sizedistribution of the hexagonal tungsten trioxide or pyrochlorenanostructures after grinding is less than 0.4, or less than 0.35 orless than 0.3, or less than 0.25, or less than 0.2, or less than 0.15,or less than 0.1, or from 0.1 to 0.2, or from 0.1 to 0.3. In someembodiments the coefficient of variation of the particle sizedistribution hexagonal tungsten trioxide or pyrochlore nanostructuresafter grinding is less than 0.6, or less than 0.55 or less than 0.5, orless than 0.45, or less than 0.4, or less than 0.35, or less than 0.3,or from 0.3 to 0.45, or from 0.3 to 0.55.

In some embodiments the mean particle size of the size-reduced hexagonaltungsten trioxide or pyrochlore nanostructures after grinding, washing,and separating from the washed contaminants, is from 50 to 300 nm, orfrom 100 to 300 nm, or from 150 to 300 nm, or from 200 to 300 nm, orfrom 250 to 300 nm, or from 100 to 250 nm, or from 50 to 250 nm, or from50 to 200 nm, or from 50 to 150 nm, or from 50 to 100, or less than 300nm, or less than 250 nm, or less than 200 nm, or less than 150 nm, orless than 100 nm. In some embodiments the median particle size of thesize-reduced hexagonal tungsten trioxide or pyrochlore nanostructuresafter grinding, washing, and separating from the washed contaminants, isfrom 50 to 300 nm, or from 100 to 300 nm, or from 150 to 300 nm, or from200 to 300 nm, or from 250 to 300 nm, or from 100 to 250 nm, or from 50to 250 nm, or from 50 to 200 nm, or from 50 to 150 nm, or from 50 to100, or less than 300 nm, or less than 250 nm, or less than 200 nm, orless than 150 nm, or less than 100 nm.

In some embodiments the polydispersity index (as defined in the ISOstandard document 13321:1996 E and ISO 22412:2008) of the particle sizedistribution of the size-reduced hexagonal tungsten trioxide orpyrochlore nanostructures after grinding, washing, and separating fromthe washed contaminants, is less than 0.4, or less than 0.35 or lessthan 0.3, or less than 0.25, or less than 0.2, or less than 0.15, orless than 0.1, or from 0.1 to 0.2, or from 0.1 to 0.3. In someembodiments the coefficient of variation of the particle sizedistribution of the size-reduced hexagonal tungsten trioxide orpyrochlore nanostructures after grinding, washing, and separating fromthe washed contaminants, is less than 0.6, or less than 0.55 or lessthan 0.5, or less than 0.45, or less than 0.4, or less than 0.35, orless than 0.3, or from 0.3 to 0.45, or from 0.3 to 0.55.

In some embodiments the mean particle size of the hexagonal tungstentrioxide or pyrochlore nanostructures after grinding, washing, and afirst grinding step is from 50 to 300 nm, or from 100 to 300 nm, or from150 to 300 nm, or from 200 to 300 nm, or from 250 to 300 nm, or from 100to 250 nm, or from 50 to 250 nm, or from 50 to 200 nm, or from 50 to 150nm, or from 50 to 100, or less than 300 nm, or less than 250 nm, or lessthan 200 nm, or less than 150 nm, or less than 100 nm. In someembodiments the polydispersity index (as defined in the ISO standarddocument 13321:1996 E and ISO 22412:2008) of the particle sizedistribution of the size-reduced hexagonal tungsten trioxide orpyrochlore nanostructures after grinding, washing, and a first grindingstep, is less than 0.4, or less than 0.35 or less than 0.3, or less than0.25, or less than 0.2, or less than 0.15, or less than 0.1, or from 0.1to 0.2, or from 0.1 to 0.3. In some embodiments the coefficient ofvariation of the particle size distribution of the size-reducedhexagonal tungsten trioxide or pyrochlore nanostructures after grinding,washing, and a first grinding step, is less than 0.6, or less than 0.55or less than 0.5, or less than 0.45, or less than 0.4, or less than0.35, or less than 0.3, or from 0.3 to 0.45, or from 0.3 to 0.55.

In some embodiments the mean particle size of the hexagonal tungstentrioxide or pyrochlore nanostructures after grinding, washing, a firstgrinding step, and a second grinding step is from 50 to 300 nm, or from100 to 300 nm, or from 150 to 300 nm, or from 200 to 300 nm, or from 250to 300 nm, or from 100 to 250 nm, or from 50 to 250 nm, or from 50 to200 nm, or from 50 to 150 nm, or from 50 to 100, or less than 300 nm, orless than 250 nm, or less than 200 nm, or less than 150 nm, or less than100 nm. In some embodiments the polydispersity index (as defined in theISO standard document 13321:1996 E and ISO 22412:2008) of the particlesize distribution of the hexagonal tungsten trioxide or pyrochlorenanostructures after grinding, washing, a first grinding step, and asecond grinding step is less than 0.4, or less than 0.35 or less than0.3, or less than 0.25, or less than 0.2, or less than 0.15, or lessthan 0.1, or from 0.1 to 0.2, or from 0.1 to 0.3. In some embodimentsthe coefficient of variation of the particle size distribution hexagonaltungsten trioxide or pyrochlore nanostructures after grinding, washing,a first grinding step, and a second grinding step is less than 0.6, orless than 0.55 or less than 0.5, or less than 0.45, or less than 0.4, orless than 0.35, or less than 0.3, or from 0.3 to 0.45, or from 0.3 to0.55.

In some embodiments, after the tungsten oxide, or tungsten trioxide, orhexagonal tungsten trioxide, or pyrochlore particles are size-reduced bygrinding, the resulting nanostructures are filtered to remove thegrinding media and any other large diameter solids. In some embodimentsthe filter pore diameter is 0.7 micron or less. In some embodiments thefilter pore diameter is 0.45 micron or less. In some embodiments thefilter pore diameter is 0.18 micron or less.

In some embodiments the tungsten oxide, or tungsten trioxide, orhexagonal tungsten trioxide, or pyrochlore nanostructures are coatedonto a substrate using slot die coating, and the wet coating thicknessis from 25 to 40 microns, or from 30 to 50 microns, or from 50 to 80microns. The concentration by mass of the solid nanostructuresdetermines what wet coating thickness is required to achieve a targetdry film thickness. In some embodiments, the dry film thickness isapproximately 1 micron, or from 0.1 to 10 microns, or from 0.5 to 1.5microns, or from 0.2 to 2 microns.

In one example, a dry film of hexagonal tungsten trioxide or pyrochlorenanostructures is targeted, which has an approximate thickness of 1micron, and an approximate capacity of 30 mC/cm². In this example, theformula used to relate the solids loading in wt % (i.e. concentration bymass) of the tungsten trioxide nanostructures ink to the target wetcoating thickness in microns to is:

Wet Thickness=[0.10/(weight % solids loading)]*37.5

Therefore, an 8 wt % solids loading ink would be coated at a wetthickness of 46.9 microns, a 10 wt % solids loading ink would be coatedat a wet thickness of 37.5 microns, and a 12 wt % solids loading inkwould be coated at a wet thickness of 31.25 microns.

In some embodiments the tungsten oxide, or tungsten trioxide, orhexagonal tungsten trioxide, or pyrochlore nanostructures are coatedonto a substrate using slot die coating, and the coating speed is from400 to 600 cm/min, or from 200 to 500 cm/min. Different solvents can beused for coating, such as water, IPA, or propylene glycol propyl ether(PGPE), and the optimal coating speed will be different for differenttypes of solvents. For example, tungsten oxide nanostructures dispersedin isopropyl alcohol (IPA) has an optimal coating speed of approximately400 cm/min, and a process window of approximately 200 to 500 cm/min. Inanother example, tungsten oxide nanostructures dispersed in PGPE has anoptimal coating speed of approximately 500 cm/min.

In some embodiments the tungsten oxide, or tungsten trioxide, orhexagonal tungsten trioxide, or pyrochlore nanostructures are coatedonto a substrate using slot die coating, and the die lip to substrategap is from 60 to 160 microns. The die lip to substrate gap is largerfor thicker desired wet coating thicknesses. In some embodiments, thedie lip to substrate gap is twice as large as the desired wet coatingthickness.

In some embodiments the tungsten oxide, or tungsten trioxide, orhexagonal tungsten trioxide, or pyrochlore nanostructures are coatedonto a substrate using slot die coating, and the gap between the diehalves is approximately 100 microns.

In some embodiments the tungsten oxide, or tungsten trioxide, orhexagonal tungsten trioxide, or pyrochlore nanostructures are coatedonto a substrate using wet coating techniques, and subsequently dried ina vacuum. If a low vapor pressure solvent is used to coat thenanostructures, then a vacuum dry can improve the uniformity and processtime required to remove the solvent. In some embodiments, propyleneglycol propyl ether (PGPE) is used as the coating solvent and vacuumdried at from approximately 150 to 200 mTorr for from approximately 1 to2 min per approximately 235 cm² area of wet coated substrate.

In some embodiments the tungsten oxide, or tungsten trioxide, orhexagonal tungsten trioxide, or pyrochlore nanostructures are coatedonto a substrate using wet coating techniques, and leveling agents areused to improve the coated film uniformity. In some embodiments, a lowvapor pressure solvent (e.g., PGPE) is used with a leveling agent with alow surface tension leveling agent (e.g., 2,3-butane diol).

In some embodiments, the thin film of hexagonal tungsten trioxide orpyrochlore nanostructures does not comprise a binder material. In someembodiments, the thin film of hexagonal tungsten trioxide or pyrochlorenanoparticles does not comprise a binder material. In some embodiments,the thin film of hexagonal tungsten trioxide or pyrochlorenanostructures size-reduced by grinding does not comprise a bindermaterial. In some embodiments, hexagonal tungsten trioxide or pyrochloreis produced via hydrothermal synthesis, a colloidal dispersion ofhexagonal tungsten trioxide or pyrochlore is produced, and then the inkis coated on a substrate to produce a thin film of tungsten trioxidenanostructures, wherein the thin film of hexagonal tungsten trioxide orpyrochlore nanostructures does not comprise a binder material. Many thinfilms formed from pluralities of nanostructures utilize a bindermaterial to improve the mechanical properties of the resulting films.Silver nanoparticles or nanowires, used for conducting lines onelectronic devices use binder materials (such as urethane acrylate,polyvinyl alcohol, gelatin, polypyrrolidone, epoxies, phenolic resins,acrylics, urethanes, silicones, styrene allyl alcohols, polyalkylenecarbonates, and/or polyvinyl acetals) to improve the electrical and/ormechanical properties of the films. [U.S. Patent Application Publication2009/0130433 A1] [WO 2013036519 A1] In some embodiments, thenanostructures described in this disclosure do not require bindermaterials to achieve good adhesion to the substrates.

In some embodiments, the substrate comprises a material with a lowmelting point, and/or a low glass transition temperature, and/or a lowsoftening point. One advantage of the methods described in someembodiments in this disclosure is that crystalline hexagonal tungstentrioxide or pyrochlore can be synthesized, and subsequently coated on asubstrate. This enables high temperature materials synthesis to impartcertain properties to the produced materials, without the need to exposethe substrate to high temperatures. In some embodiments, the substrateis exposed to a maximum temperature of 50° C., or a maximum temperatureof 100° C., or a maximum temperature of 150° C., or a maximumtemperature of 200° C., or a maximum temperature of 250° C., or amaximum temperature of 300° C., or a maximum temperature of 350° C., ora maximum temperature of 400° C., or a maximum temperature of 450° C.,or a maximum temperature of 500° C. In some embodiments, the substratecomprises a material with a melting point less than 800° C., or lessthan 700° C., or less than 600° C., or less than 500° C., or less than400° C., or less than 300° C., or less than 250° C., or less than 200°C., or less than 150° C., or less than 100° C., or from 100° C. to 200°C., or from 200° C. to 300° C., or from 300° C. to 400° C., or from 400°C. to 500° C., or from 500° C. to 600° C., or from 600° C. to 700° C.,or from 700° C. to 800° C., or from 800° C. to 900° C., or from 900° C.to 1000° C., or from 1000° C. to 1100° C., or from 1100° C. to 1200° C.,or from 1200° C. to 1300° C., or from 1300° C. to 1400° C., or from1400° C. to 1500° C., or from 1500° C. to 1600° C., or a glasstransition temperature less than 1000° C., or less than 900° C., or lessthan 800° C., or less than 700° C., or less than 600° C., or less than500° C., or less than 400° C., or less than 300° C., or less than 250°C., or less than 200° C., or less than 150° C., or less than 100° C., orfrom 75° C. to 125° C., or from 125° C. to 175° C., or from 175° C. to225° C., or from 225° C. to 275° C., or from 275° C. to 325° C., or from325° C. to 375° C., or from 375° C. to 425° C., or from 425° C. to 500°C., or from 500° C. to 600° C., or from 600° C. to 700° C., or from 700°C. to 800° C., or from 800° C. to 900° C., or a softening point lessthan 1000° C., or less than 900° C., or less than 800° C., or less than700° C., or less than 600° C., or less than 500° C., or less than 400°C., or less than 300° C., or less than 250° C., or less than 200° C., orless than 150° C., or less than 100° C., or from 75° C. to 125° C., orfrom 125° C. to 175° C., or from 175° C. to 225° C., or from 225° C. to275° C., or from 275° C. to 325° C., or from 325° C. to 375° C., or from375° C. to 425° C., or from 425° C. to 500° C., or from 500° C. to 600°C., or from 600° C. to 700° C., or from 700° C. to 800° C., or from 800°C. to 900° C.

The tungsten oxide, or tungsten trioxide, or hexagonal tungstentrioxide, or pyrochlore nanoparticles described in this disclosure canbe deposited onto substrates using many different methods. For example,tungsten oxide nanoparticles can be deposited by wet coating techniques,such as spin, dip, spray, gravure, slot, roll, and ink-jet coating. Insome embodiments, these methods can be used to deposit tungsten oxidenanoparticle films onto individual substrates. In some embodiments,these methods can be used to deposit tungsten oxide nanoparticle filmsin a continuous roll-to-roll process. In some embodiments, the films aredeposited in a low-particle clean room environment. In some embodiments,the solvent for the tungsten oxide nanoparticles can be evaporated inair at room temperature, or the coating solvent can be removed usingapplied heat, or vacuum, or both applied heat and vacuum. In someembodiments, a post deposition heat treatment can be used, in an air, orinert, or reactive environment. In some embodiments, the depositedtungsten oxide nanoparticle film is unreactive with oxygen and/ormoisture. In some embodiments, the deposited tungsten oxide nanoparticlefilm is maintained in an inert environment (e.g., humidity controlledair or nitrogen) to avoid undesirable reactions with oxygen and/ormoisture.

Electrochromic Multi-Layer Stacks with Tungsten Oxide Nanostructureswith Large Channels

FIG. 2 depicts a cross-sectional structural diagram of electrochromicdevice 1 according to a first embodiment of the present disclosure.Moving outward from the center, electrochromic device 1 comprises an ionconductor layer 10. First electrode layer 20 is on one side of and incontact with a first surface of ion conductor layer 10, and secondelectrode layer 21 is on the other side of and in contact with a secondsurface of ion conductor layer 10. In addition, at least one of firstand second electrode layers 20, 21 comprises electrochromic material; inone embodiment, first and second electrode layers 20, 21 each compriseelectrochromic material. The central structure, that is, layers 20, 10,21, is positioned between first and second electrically conductivelayers 22 and 23 which, in turn, are arranged against “outer substrates”24, 25. Elements 22, 20, 10, 21, and 23 are collectively referred to asan electrochromic stack 28.

Electrically conductive layer 22 is in electrical contact with oneterminal of a power supply (not shown) via bus bar 26 and electricallyconductive layer 23 is in electrical contact with the other terminal ofa power supply (not shown) via bus bar 27 whereby the transmissivity ofthe electrochromic stack 28 may be changed by applying a voltage pulseto electrically conductive layers 22 and 23. The pulse causes electronsand ions to move between first and second electrode layers 20 and 21and, as a result, electrochromic material in the first and/or secondelectrode layer(s) change(s) optical states, thereby switchingelectrochromic stack 28 from a more transmissive state to a lesstransmissive state, or from a less transmissive state to a moretransmissive state. In one embodiment, electrochromic stack 28 istransparent before the voltage pulse and less transmissive (e.g., morereflective or colored) after the voltage pulse or vice versa.

It should be understood that the reference to a transition between aless transmissive and a more transmissive state is non-limiting and isintended to describe the entire range of transitions attainable byelectrochromic materials to the transmissivity of electromagneticradiation. For example, the change in transmissivity may be a changefrom a first optical state to a second optical state that is (i)relatively more absorptive (i.e., less transmissive) than the firststate, (ii) relatively less absorptive (i.e., more transmissive) thanthe first state, (iii) relatively more reflective (i.e., lesstransmissive) than the first state, (iv) relatively less reflective(i.e., more transmissive) than the first state, (v) relatively morereflective and more absorptive (i.e., less transmissive) than the firststate or (vi) relatively less reflective and less absorptive (i.e., moretransmissive) than the first state. Additionally, the change may bebetween the two extreme optical states attainable by an electrochromicdevice, e.g., between a first transparent state and a second state, thesecond state being opaque or reflective (mirror). Alternatively, thechange may be between two optical states, at least one of which isintermediate along the spectrum between the two extreme states (e.g.,transparent and opaque or transparent and mirror) attainable for aspecific electrochromic device. Unless otherwise specified herein,whenever reference is made to a less transmissive and a moretransmissive, or even a bleached-colored transition, the correspondingdevice or process encompasses other optical state transitions such asnon-reflective-reflective, transparent-opaque, etc. Further, the term“bleached” may refer to an optically neutral state, e.g., uncolored,transparent or translucent. Still further, unless specified otherwiseherein, the “color” of an electrochromic transition is not limited toany particular wavelength or range of wavelengths. As understood bythose of skill in the art, the choice of appropriate electrochromic andcounter electrode materials governs the relevant optical transition.

In general, the change in transmissivity preferably comprises a changein transmissivity to electromagnetic radiation having a wavelength inthe range of infrared to ultraviolet radiation. For example, in oneembodiment the change in transmissivity is predominately a change intransmissivity to electromagnetic radiation in the infrared spectrum. Ina second embodiment, the change in transmissivity is to electromagneticradiation having wavelengths predominately in the visible spectrum. In athird embodiment, the change in transmissivity is to electromagneticradiation having wavelengths predominately in the ultraviolet spectrum.In a fourth embodiment, the change in transmissivity is toelectromagnetic radiation having wavelengths predominately in theultraviolet and visible spectra. In a fifth embodiment, the change intransmissivity is to electromagnetic radiation having wavelengthspredominately in the infrared and visible spectra. In a sixthembodiment, the change in transmissivity is to electromagnetic radiationhaving wavelengths predominately in the ultraviolet, visible andinfrared spectra.

Electrochromic Multi-Layer Stacks with Tungsten Oxide Cathodes

This disclosure describes an electrochromic multi-layer stack comprisinga thin film comprising hexagonal tungsten trioxide or pyrochlorenanostructures, an electrically conductive layer, and an outersubstrate. This disclosure also describes a method to produce a thinfilm of hexagonal tungsten trioxide or pyrochlore, wherein hexagonaltungsten trioxide or pyrochlore particles are synthesized, size-reducedby grinding to produce hexagonal tungsten trioxide or pyrochlorenanostructures, formulated into an ink, and coated on a substrate toproduce a thin film of hexagonal tungsten trioxide or pyrochlore.

In some embodiments (FIG. 2), the electrochromic multi-layer stackcomprises outer substrates 24, 25; electrically conductive layers 22,23; electrodes 20, 21 comprising an electrochromic cathode comprising athin film comprising hexagonal tungsten trioxide nanostructures, and amatched electrochromic anode; and an ion conductor layer 10. In someembodiments, an electrochromic device comprises the electrochromicmulti-layer stack comprising hexagonal tungsten trioxide or pyrochlorenanostructures described above.

Oxides of W, Nb, Ta, Ti, V, and Mo color under charge insertion(reduction) and are referred to as cathodic electrochromic materials.Oxides of Ni, Cr, Mn and Ir color upon charge extraction (oxidation) andare anodic electrochromic materials. In one embodiment, cathodicallycoloring films include oxides based on tungsten, molybdenum, niobium,and titanium.

In some embodiments, the cathode of an electrochromic multi-layer stackcomprises hexagonal tungsten trioxide or pyrochlore. In someembodiments, the cathode of an electrochromic multi-layer stackcomprises hexagonal tungsten trioxide or pyrochlore synthesized byhydrothermal synthesis.

In some embodiments, a method of producing the cathode of anelectrochromic multi-layer stack comprises synthesizing hexagonaltungsten trioxide particles by hydrothermal synthesis; size-reducing thehexagonal tungsten trioxide particles by grinding to produce crystallinehexagonal tungsten trioxide nanostructures; and coating the hexagonaltungsten trioxide nanostructures on a substrate. In some embodiments, amethod of producing the cathode of an electrochromic multi-layer stackcomprises synthesizing pyrochlore particles by hydrothermal synthesis;size-reducing the pyrochlore particles by grinding to producecrystalline pyrochlore nanostructures; and coating the pyrochlorenanostructures on a substrate. In some embodiments, a method ofproducing the cathode of an electrochromic multi-layer stack comprisessynthesizing hexagonal tungsten trioxide particles by hydrothermalsynthesis; size-reducing the hexagonal tungsten trioxide particles bygrinding to produce crystalline hexagonal tungsten trioxidenanostructures; and coating the hexagonal tungsten trioxidenanostructures on a substrate, without the addition of a binder. In someembodiments, a method of producing the cathode of an electrochromicmulti-layer stack comprises synthesizing pyrochlore particles byhydrothermal synthesis; size-reducing the pyrochlore particles bygrinding to produce crystalline pyrochlore nanostructures; and coatingthe pyrochlore nanostructures on a substrate, without the addition of abinder.

In some embodiments, a method of producing the cathode of anelectrochromic multi-layer stack comprises synthesizing hexagonaltungsten trioxide or pyrochlore particles by hydrothermal synthesis;size-reducing the hexagonal tungsten trioxide or pyrochlore particles bygrinding to produce crystalline hexagonal tungsten trioxide orpyrochlore nanostructures; and coating the hexagonal tungsten trioxideor pyrochlore nanostructures on a substrate, wherein the substrate has amelting point less than 800° C., or less than 700° C., or less than 600°C., or less than 500° C., or less than 400° C., or less than 300° C., orless than 250° C., or less than 200° C., or less than 150° C., or lessthan 100° C., or from 100° C. to 200° C., or from 200° C. to 300° C., orfrom 300° C. to 400° C., or from 400° C. to 500° C., or from 500° C. to600° C., or from 600° C. to 700° C., or from 700° C. to 800° C., or from800° C. to 900° C., or from 900° C. to 1000° C., or from 1000° C. to1100° C., or from 1100° C. to 1200° C., or from 1200° C. to 1300° C., orfrom 1300° C. to 1400° C., or from 1400° C. to 1500° C., or from 1500°C. to 1600° C. In some embodiments, a method of producing the cathode ofan electrochromic multi-layer stack comprises synthesizing hexagonaltungsten trioxide or pyrochlore particles by hydrothermal synthesis;size-reducing the hexagonal tungsten trioxide or pyrochlore particles bygrinding to produce crystalline hexagonal tungsten trioxide orpyrochlore nanostructures; and coating the hexagonal tungsten trioxideor pyrochlore nanostructures on a substrate, wherein the substrate has aglass transition temperature less than 1000° C., or less than 900° C.,or less than 800° C., or less than 700° C., or less than 600° C., orless than 500° C., or less than 400° C., or less than 300° C., or lessthan 250° C., or less than 200° C., or less than 150° C., or less than100° C., or from 75° C. to 125° C., or from 125° C. to 175° C., or from175° C. to 225° C., or from 225° C. to 275° C., or from 275° C. to 325°C., or from 325° C. to 375° C., or from 375° C. to 425° C., or from 425°C. to 500° C., or from 500° C. to 600° C., or from 600° C. to 700° C.,or from 700° C. to 800° C., or from 800° C. to 900° C. In someembodiments, a method of producing the cathode of an electrochromicmulti-layer stack comprises synthesizing hexagonal tungsten trioxide orpyrochlore particles by hydrothermal synthesis; size-reducing thehexagonal tungsten trioxide or pyrochlore particles by grinding toproduce crystalline hexagonal tungsten trioxide or pyrochlorenanostructures; and coating the hexagonal tungsten trioxide orpyrochlore nanostructures on a substrate, wherein the substrate has asoftening point less than 1000° C., or less than 900° C., or less than800° C., or less than 700° C., or less than 600° C., or less than 500°C., or less than 400° C., or less than 300° C., or less than 250° C., orless than 200° C., or less than 150° C., or less than 100° C., or from75° C. to 125° C., or from 125° C. to 175° C., or from 175° C. to 225°C., or from 225° C. to 275° C., or from 275° C. to 325° C., or from 325°C. to 375° C., or from 375° C. to 425° C., or from 425° C. to 500° C.,or from 500° C. to 600° C., or from 600° C. to 700° C., or from 700° C.to 800° C., or from 800° C. to 900° C.

In some embodiments, a method of producing the cathode of anelectrochromic multi-layer stack comprises synthesizing hexagonaltungsten trioxide or pyrochlore particles by hydrothermal synthesis;size-reducing the hexagonal tungsten trioxide or pyrochlore particles bygrinding to produce crystalline hexagonal tungsten trioxide orpyrochlore nanostructures; and coating the hexagonal tungsten trioxideor pyrochlore nanostructures on a substrate, wherein the substrate isthicker than 50 microns.

In some embodiments, a method of producing the cathode of anelectrochromic multi-layer stack comprises synthesizing hexagonaltungsten trioxide or pyrochlore particles by hydrothermal synthesis;size-reducing the hexagonal tungsten trioxide or pyrochlore particles bygrinding to produce crystalline hexagonal tungsten trioxide orpyrochlore nanostructures; and coating the hexagonal tungsten trioxideor pyrochlore nanostructures on a substrate, wherein the substratecomprises an electrically conducting layer and outer substrate, and thematerial of the outer substrate is selected from the group consistingof: glass (e.g. soda lime glass or borosilicate glass), and plastic(e.g. polycarbonates, polyacrylics, polyurethanes, urethane carbonatecopolymers, polysulfones, polyimides, polyacrylates, polyethers,polyester, polyethylenes, polyalkenes, polyimides, polysulfides,polyvinylacetates and cellulose-based polymers).

In some embodiments, a method of producing the cathode of anelectrochromic multi-layer stack comprises synthesizing hexagonaltungsten trioxide or pyrochlore particles by hydrothermal synthesis;size-reducing the hexagonal tungsten trioxide or pyrochlore particles bygrinding to produce crystalline hexagonal tungsten trioxide orpyrochlore nanostructures; and coating the hexagonal tungsten trioxideor pyrochlore nanostructures on a substrate, wherein the substratecomprises an electrically conducting layer and outer substrate, and thematerial of the electrically conductive layer is selected from a groupconsisting of: transparent conductive oxides, thin metallic coatings,networks of conductive nanoparticles (e.g., rods, tubes, dots),conductive metal nitrides, and composite conductors.

A tungsten trioxide, or hexagonal tungsten trioxide, or pyrochlorecathode in an EC multi-layer stack is intercalated and deintercalatedwith a cation (e.g. H⁺, Li⁺ or Na⁺) during switching. In someembodiments, the formula of tungsten oxide, or hexagonal tungstentrioxide, or pyrochlore upon intercalation is A_(y)W_(1−x)M_(x)O_(3±z),where A is a Group IA element, M is an octahedrally coordinated metal, xhas a value from 0.0 to 1.0, y has a value of 0 to 1 and z has a valuefrom 0.0 to 0.3.

Intercalation of cations (e.g. H+ or Li+) causes the reduction oftungsten (e.g., W⁶⁺ converting to W⁵⁺ and/or W⁴⁺), which in turn reducesthe transmission of the material. This is what occurs, for instance, tothe cathode during the switching of an electrochromic device from ableached state to a darkened state. Therefore certain cation impuritiesin the as-deposited film will degrade the transmission of the film,which is undesirable in certain applications (e.g., in cathodes ofelectrochromic devices). In some embodiments, the value of z in theas-deposited film is from about 0.0 to about 0.05, or from about 0.05 toabout 0.1, or from about 0.0 to about 0.2 depending on the exact valueof y. For example, if a material such as Na_(0.25)WO_(3±z) is prepared,then z may be understood to be 0.125. In some embodiments, excess oxygenis incorporated in greater amounts that do not degrade the transmissionand z can be greater than 0.2, or greater than 0.3, or greater than 0.4,or greater than 0.5. In some embodiments, k should be 0 or as close to 0as feasible to avoid photochemical degradation mechanisms. In someembodiments the value of k is less important. It is understood that theband gap of the material prepared will be relevant to whether thepresence of water (and whether k does or does not equal zero) isimportant. In some embodiments, the tungsten oxide film will beincorporated into an electrochromic multi-layer stack, or anelectrochromic device, and a mobile cation is added (e.g., Li⁺). In someembodiments, the mobile cation is introduced in an ion conductor layer.In some embodiments, the tungsten oxide is incorporated into anelectrochromic device, and is subsequently reduced (e.g., by switchingthe electrochromic device to a darkened state), wherein the mobilecation will be intercalated into the tungsten oxide, and y will beincreased to a value from about 0.1 to about 0.5, or from about 0.1 toabout 0.7, or from about 0.1 to about 1.0, or from about 0.3 to about0.5, or from about 0.3 to about 0.7, or from about 0.3 to about 1.0. Inelectrochromic devices, such as architectural windows, this reaction isreversible.

Electrochromic Multi-Layer Stack Ion Conductors

Ion conductor layer 10 serves as a medium through which ions aretransported (in the manner of an electrolyte) when the electrochromicdevice switches between an optically less transmissive (“colored”) stateand an optically more transmissive (“bleached”) state. Stateddifferently, the ion conducting layer permits sufficient ionicconduction between the first and second electrode layers 20, 21 upon theapplication of a voltage across electrochromic stack 28. Depending onthe choice of materials, such ions include lithium ions (Li+) andhydrogen ions (H+) (i.e., protons). Other ions may also be employed incertain embodiments. These include deuterium ions (D+), sodium ions(Na+), potassium ions (K+), rubidium ions (Rb+), cesium ions (Cs+),ammonium ions (NH4+), calcium ions (Ca++), barium ions (Ba++), strontiumions (Sr++), magnesium ions (Mg++) or others. In one embodiment, ionconductor layer 10 has a lithium ion conductivity of at least about 10⁻⁵S/cm at room temperature (i.e., 25° C.). For example, in one suchembodiment, ion conductor layer 10 has a lithium ion conductivity of atleast about 10⁻⁴ S/cm at room temperature. By way of further example, inone such embodiment ion conductor layer 10 has a lithium ionconductivity of at least about 10⁻³ S/cm at room temperature. By way offurther example, in one such embodiment ion conductor layer 10 has alithium ion conductivity of at least about 10⁻² S/cm at roomtemperature. Preferably, ion conductor layer 10 has sufficiently lowelectron conductivity that negligible electron transfer takes placeduring normal operation.

Ion conductor layer 10 is also preferably sufficiently durable so as towithstand repeated cycling of the electrochromic device between anoptically less transmissive state and an optically more transmissivestate. For example, in one such embodiment, lithium ion conductivity ofion conductor layer 10 varies less than about 5% upon cycling of theelectrochromic device between a less transmissive state (e.g. about 5%transmissive) and a more transmissive state (e.g. about 70%transmissive) for at least 100 hours at 85° C. By way of furtherexample, in one such embodiment lithium ion conductivity of ionconductor layer 10 varies less than about 4% upon cycling of theelectrochromic device between a less transmissive state and a moretransmissive state for at least 100 hours at 85° C. By way of furtherexample, in one such embodiment lithium ion conductivity of ionconductor layer 10 varies less than about 3% upon cycling of theelectrochromic device between a less transmissive state and a moretransmissive state for at least 100 hours at 85° C. By way of furtherexample, in one such embodiment lithium ion conductivity of ionconductor layer 10 varies less than about 2% upon cycling of theelectrochromic device between a less transmissive state and a moretransmissive state for at least 100 hours at 85° C. By way of furtherexample, in one such embodiment lithium ion conductivity of ionconductor layer 10 varies less than about 1% upon cycling of theelectrochromic device between a less transmissive state and a moretransmissive state for at least 100 hours at 85° C. By way of furtherexample, in one such embodiment lithium ion conductivity of ionconductor layer 10 varies less than about 0.5% upon cycling of theelectrochromic device between a less transmissive state and a moretransmissive state for at least 100 hours at 85° C.

Additionally, to enable electrochromic stack 28 to endure a range ofphysical stresses to which it may be exposed during the manufacture ofelectrochromic device 1, its incorporation into a structure (e.g., anautomobile, aircraft, or building), and/or its intended end-useenvironment (e.g., as an architectural window, sunroof, skylight,mirror, etc., in such a structure), ion conductor layer 10 alsopossesses sufficient cohesion and adhesion to the first and secondelectrode layers 20, 21. For example, in one embodiment, ion conductorlayer 10 has a lap shear strength of at least 100 kPa, as measured at1.27 mm/min, at room temperature, in accordance with ASTM Internationalstandard D1002 or D3163. For example, in one embodiment ion conductorlayer 10 has a lap shear strength of at least 200 kPa. By way of furtherexample, in one such embodiment ion conductor layer 10 has a lap shearstrength of at least 300 kPa. By way of further example, in one suchembodiment ion conductor layer 10 has a lap shear strength of at least400 kPa. By way of further example, in one such embodiment ion conductorlayer 10 has a lap shear strength of at least 500 kPa. By way of furtherexample, in one such embodiment ion conductor layer 10 has a lap shearstrength of at least 600 kPa. Preferably, ion conductor layer 10 iselastically deformable. In one exemplary embodiment, ion conductor layer10 has an elongation to failure of at least 1 mm.

Some non-exclusive examples of electrolytes typically incorporated intoion conductor layer 10 are: solid polymer electrolytes (SPE), such aspoly(ethylene oxide) with a dissolved lithium salt; gel polymerelectrolytes (GPE), such as mixtures of poly(methyl methacrylate) andpropylene carbonate with a lithium salt; composite gel polymerelectrolytes (CGPE) that are similar to GPE's but with an addition of asecond polymer such a poly(ethylene oxide), and liquid electrolytes (LE)such as a solvent mixture of ethylene carbonate/diethyl carbonate with alithium salt; and composite organic-inorganic electrolytes (CE),comprising an LE with an addition of titania, silica or other oxides.Some non-exclusive examples of lithium salts used areLiTFSI—CF₃SO₂NLiSO₂CF₃ (lithium bis(trifluoromethane) sulfonimide),LiBF₄ (lithium tetra fluoroborate), LiAsF₆ (lithium hexafluoroarsenate), LiCF₃SO₃ (lithium trifluoromethane sulfonate), and LiClO₄(lithium perchlorate). Additional examples of suitable ion conductinglayers include silicates, silicon oxides, tungsten oxides, tantalumoxides, niobium oxides, and borates. The silicon oxides includesilicon-aluminum-oxide. These materials may be doped with differentdopants, including lithium. Lithium doped silicon oxides include lithiumsilicon aluminum-oxide. In some embodiments, the ion conducting layercomprises a silicate based structure. In other embodiments, suitable ionconductors particularly adapted for lithium ion transport include, butare not limited to, lithium silicate, lithium aluminum silicate, lithiumaluminum borate, lithium aluminum fluoride, lithium borate, lithiumnitride, lithium zirconium silicate, lithium niobate, lithiumborosilicate, lithium phosphosilicate, and other such lithium-basedceramic materials, silicas, or silicon oxides, including lithiumsilicon-oxide.

Electrochromic Multi-Layer Stack Anodes

In one embodiment, the electrochromic materials comprised by the anodeelectrode (i.e., the first or second electrode 20, 21; see FIG. 2) of amulti-layer stack of the present disclosure are inorganic ororganometallic and the electrochromic materials comprised by the cathode(i.e., the other of the first or second electrode 20, 21; see FIG. 2)are independently inorganic or organometallic. More specifically, theelectrochromic materials comprised by the anode and/or the cathode areinorganic or organometallic solid state materials with 3-D frameworkstructures comprising metals bridged or separated by anionic atoms orligands such as oxide, hydroxide, phosphate, cyanide, halide, thatfurther comprise mobile ions such as protons, lithium, sodium, potassiumthat can intercalate and de-intercalate as the material is reduced oroxidized during the electrochromic cycle.

A variety of anodically coloring films comprising Ni, Ir, and Fe areknown in the art and can be prepared by a number of deposition processesincluding vapor deposition processes, wet-coating processes, spraycoating processes, dip coating, and electrodeposition. Many of theseanodic films are mixed metal oxides where lithium or protons areintercalated to balance charge during cycling. Additionally, non-oxidebased films such as Prussian blue materials can be useful as anodicelectrochromic films. In one embodiment, anodically coloring filmsinclude oxides, hydroxides and/or oxy-hydrides based on nickel, iridium,iron, chromium, cobalt and/or rhodium.

Electrochromic Multi-Layer Stack Substrates

The “substrate” comprises an electrically conductive layer 22, 23, andan “outer substrate” 24, 25. In some embodiments, the electricallyconductive layer is selected from a group consisting of: transparentconductive oxides, thin metallic coatings, networks of conductivenanoparticles (e.g., rods, tubes, dots), conductive metal nitrides, andcomposite conductors.

In some embodiments, the outer substrate is selected from a groupconsisting of: glass (e.g. soda lime glass or borosilicate glass), andplastic (e.g. polycarbonates, polyacrylics, polyurethanes, urethanecarbonate copolymers, polysulfones, polyimides, polyacrylates,polyethers, polyester, polyethylenes, polyalkenes, polyimides,polysulfides, polyvinylacetates and cellulose-based polymers).

Electrochromic Devices Containing Tungsten Oxide Thin Films

The thickness of the ion conductor layer 10 will vary depending on thematerial. In some embodiments using an inorganic ion conductor, the ionconductor layer 10 is about 250 nm to 1 nm thick, preferably about 50 nmto 5 nm thick. In some embodiments using an organic ion conductor, theion conductor layer is about 1000000 nm to 1000 nm thick or about 250000nm to 10000 nm thick. The thickness of the ion conductor layer is alsosubstantially uniform. In one embodiment, a substantially uniform ionconductor layer varies by not more than about +/−10% in each of theaforementioned thickness ranges. In another embodiment, a substantiallyuniform ion conductor layer varies by not more than about +/−5% in eachof the aforementioned thickness ranges. In another embodiment, asubstantially uniform ion conductor layer varies by not more than about+/−3% in each of the aforementioned thickness ranges.

In one embodiment, the ion-conducting film is produced from the ionconducting formulation by depositing the liquid formulation with theanode film, cathode film, or both films in a sufficient quantity to forma continuous pre-crosslinked film having a uniform thickness between 50and 500 microns between the anode and cathode plates. This assembly maythen be placed in a vacuum laminator and heated under vacuum to form asealed assembly. Polymerization of the monomer/comonomer may beinitiated either thermally or photochemically. In one embodiment, anythermal processing of the device, particularly one where the substrateis plastic, is below the temperature of 200° C., and more particularly150° C., and even more particularly 100° C.

Alternatively, free standing, fully formulated ion-conducting films maybe used in place of the crosslinking IC formulation or the liquid ICformulation may be used in a “cast in place” process where a pre-formedcavity between the anode and cathode is produced (edge sealed) and theformulation is forced into this cavity through fill ports.

The thickness of anode layer 20 and cathode layer 21 will depend uponthe electrochromic material selected for the electrochromic layer andthe application. In some embodiments, anode layer 20 will have athickness in the range of about 25 nm to about 2000 nm. For example, inone embodiment anode layer 20 has a thickness of about 50 nm to about2000 nm. By way of further example, in one embodiment anode layer 20 hasa thickness of about 25 nm to about 1000 nm. By way of further example,in one such embodiment, anode layer 20 has an average thickness betweenabout 100 nm and about 700 nm. In some embodiments, anode layer 20 has athickness of about 250 nm to about 500 nm. Cathode layer 21 willtypically have thicknesses in the same ranges as those stated for anodelayer 20. One of skill in the art will appreciate that certainrelationships exist between the thickness of the anode or cathode layer,and the materials deposited to comprise the anode or cathode layer. Forexample, if the average thickness of the anode or cathode layer isbetween about 250 nm to about 500 nm, then anode or cathode precursormaterials that comprise the liquid mixtures used to deposit the anode orcathode layers will likely be composed of species that are smaller than250 nm to 500 nm.

Electrically conductive layer 22 is in electrical contact with oneterminal of a power supply (not shown) via bus bar 26 and electricallyconductive layer 23 is in electrical contact with the other terminal ofa power supply (not shown) via bus bar 27 whereby the transmissivity ofelectrochromic device 1 may be changed by applying a voltage pulse toelectrically conductive layers 22 and 23. The pulse causes electrons andions to move between anode layer 20 and cathode layer 21 and, as aresult, the anode layer 20 and, optionally, cathode layer 21 change(s)optical states, thereby switching electrochromic device 1 from a moretransmissive state to a less transmissive state, or from a lesstransmissive state to a more transmissive state. In one embodiment,electrochromic device 1 is transparent before the voltage pulse and lesstransmissive (e.g., more reflective or colored) after the voltage pulseor vice versa.

Referring again to FIG. 2, the power supply (not shown) connected to busbars 26, 27 is typically a voltage source with optional current limitsor current control features and may be configured to operate inconjunction with local thermal, photosensitive or other environmentalsensors. The voltage source may also be configured to interface with anenergy management system, such as a computer system that controls theelectrochromic device according to factors such as the time of year,time of day, and measured environmental conditions. Such an energymanagement system, in conjunction with large area electrochromic devices(e.g., an electrochromic architectural window), can dramatically lowerthe energy consumption of a building.

At least one of the substrates 24, 25 is preferably transparent, inorder to reveal the electrochromic properties of the stack 28 to thesurroundings. Any material having suitable optical, electrical, thermal,and mechanical properties may be used as first substrate 24 or secondsubstrate 25. Such substrates include, for example, glass, plastic,metal, and metal coated glass or plastic. Non-exclusive examples ofpossible plastic substrates are polycarbonates, polyacrylics,polyurethanes, urethane carbonate copolymers, polysulfones, polyimides,polyacrylates, polyethers, polyester, polyethylenes, polyalkenes,polyimides, polysulfides, polyvinylacetates and cellulose-basedpolymers. If a plastic substrate is used, it may be barrier protectedand abrasion protected using a hard coat of, for example, a diamond-likeprotective coating, a silica/silicone anti-abrasion coating, or thelike, such as is well known in the plastic glazing art. Suitable glassesinclude either clear or tinted soda lime glass, chemically tempered sodalime glass, heat strengthened soda lime glass, tempered glass, orborosilicate glass. In some embodiments of electrochromic device 1 withglass, e.g. soda lime glass, used as first substrate 24 and/or secondsubstrate 25, there is a sodium diffusion barrier layer (not shown)between first substrate 24 and first electrically conductive layer 22and/or between second substrate 25 and second electrically conductivelayer 23 to prevent the diffusion of sodium ions from the glass intofirst and/or second electrically conductive layer 23. In someembodiments, second substrate 25 is omitted.

Independent of application, the electrochromic structures of the presentdisclosure may have a wide range of sizes. In general, it is preferredthat the electrochromic device comprise a substrate having a surfacewith a surface area of at least 0.001 meter². For example, in certainembodiments, the electrochromic device comprises a substrate having asurface with a surface area of at least 0.01 meter², or at least 0.1meter², or at least 1 meter², or at least 5 meter², or at least 10meter².

At least one of the two electrically conductive layers 22, 23 is alsopreferably transparent in order to reveal the electrochromic propertiesof the stack 28 to the surroundings. In one embodiment, electricallyconductive layer 23 is transparent. In another embodiment, electricallyconductive layer 22 is transparent. In another embodiment, electricallyconductive layers 22, 23 are each transparent. In certain embodiments,one or both of the electrically conductive layers 22, 23 is inorganicand/or solid. Electrically conductive layers 22 and 23 may be made froma number of different transparent materials, including transparentconductive oxides, thin metallic coatings, networks of conductivenanoparticles (e.g., rods, tubes, dots), conductive metal nitrides, andcomposite conductors. Transparent conductive oxides include metal oxidesand metal oxides doped with one or more metals. Examples of such metaloxides and doped metal oxides include indium oxide, indium tin oxide,doped indium oxide, tin oxide, doped tin oxide, zinc oxide, aluminumzinc oxide, doped zinc oxide, ruthenium oxide, doped ruthenium oxide andthe like. Transparent conductive oxides are sometimes referred to as(TCO) layers. Thin metallic coatings that are substantially transparentmay also be used. Examples of metals used for such thin metalliccoatings include gold, platinum, silver, aluminum, nickel, and alloys ofthese. Examples of transparent conductive nitrides include titaniumnitrides, tantalum nitrides, titanium oxynitrides, and tantalumoxynitrides. Electrically conducting layers 22 and 23 may also betransparent composite conductors. Such composite conductors may befabricated by placing highly conductive ceramic and metal wires orconductive layer patterns on one of the faces of the substrate and thenover-coating with transparent conductive materials such as doped tinoxides or indium tin oxide. Ideally, such wires should be thin enough asto be invisible to the naked eye (e.g., about 100 μm or thinner).Non-exclusive examples of electron conductors 22 and 23 transparent tovisible light are thin films of indium tin oxide (ITO), tin oxide, zincoxide, titanium oxide, n- or p-doped zinc oxide and zinc oxyfluoride.Metal-based layers, such as ZnS/Ag/ZnS and carbon nanotube layers havebeen recently explored as well. Depending on the particular application,one or both electrically conductive layers 22 and 23 may be made of orinclude a metal grid.

The thickness of the electrically conductive layer may be influenced bythe composition of the material comprised within the layer and itstransparent character. In some embodiments, electrically conductivelayers 22 and 23 are transparent and each have a thickness that isbetween about 1000 nm and about 50 nm. In some embodiments, thethickness of electrically conductive layers 22 and 23 is between about500 nm and about 100 nm. In other embodiments, the electricallyconductive layers 22 and 23 each have a thickness that is between about400 nm and about 200 nm. In general, thicker or thinner layers may beemployed so long as they provide the necessary electrical properties(e.g., conductivity) and optical properties (e.g., transmittance). Forcertain applications it will generally be preferred that electricallyconductive layers 22 and 23 be as thin as possible to increasetransparency and to reduce cost.

Referring again to FIG. 2, the function of the electrically conductivelayers is to apply the electric potential provided by a power supplyover the entire surface of the electrochromic stack 28 to interiorregions of the stack. The electric potential is transferred to theconductive layers though electrical connections to the conductivelayers. In some embodiments, bus bars, one in contact with firstelectrically conductive layer 22 and one in contact with secondelectrically conductive layer 23 provide the electrical connectionbetween the voltage source and the electrically conductive layers 22 and23.

In one embodiment, the sheet resistance, R_(s), of the first and secondelectrically conductive layers 22 and 23 is about 500Ω/□ to 1Ω/□. Insome embodiments, the sheet resistance of first and second electricallyconductive layers 22 and 23 is about 100Ω/□ to 5Ω/□. In general, it isdesirable that the sheet resistance of each of the first and secondelectrically conductive layers 22 and 23 be about the same. In oneembodiment, first and second electrically conductive layers 22 and 23each have a sheet resistance of about 20Ω/□ to about 8Ω/□.

In some embodiments, the cathode of an electrochromic device compriseshexagonal tungsten trioxide or pyrochlore. In some embodiments, thecathode of an electrochromic device comprises hexagonal tungstentrioxide or pyrochlore synthesized by hydrothermal synthesis.

In some embodiments, a method of producing the cathode of anelectrochromic device comprises synthesizing hexagonal tungsten trioxideor pyrochlore particles by hydrothermal synthesis; size-reducing thehexagonal tungsten trioxide or pyrochlore particles by grinding toproduce crystalline hexagonal tungsten trioxide or pyrochlorenanostructures; and coating the hexagonal tungsten trioxide orpyrochlore nanostructures on a substrate. In some embodiments, a methodof producing the cathode of an electrochromic device comprisessynthesizing hexagonal tungsten trioxide or pyrochlore particles byhydrothermal synthesis; size-reducing the hexagonal tungsten trioxide orpyrochlore particles by grinding to produce crystalline hexagonaltungsten trioxide or pyrochlore nanostructures; and coating thehexagonal tungsten trioxide or pyrochlore nanostructures on a substrate,without the addition of a binder.

In some embodiments, a method of producing the cathode of anelectrochromic device comprises synthesizing hexagonal tungsten trioxideor pyrochlore particles by hydrothermal synthesis; size-reducing thehexagonal tungsten trioxide or pyrochlore particles by grinding toproduce crystalline hexagonal tungsten trioxide or pyrochlorenanostructures; and coating the hexagonal tungsten trioxide orpyrochlore nanostructures on a substrate, wherein the substrate has amelting point less than 800° C., or less than 700° C., or less than 600°C., or less than 500° C., or less than 400° C., or less than 300° C., orless than 250° C., or less than 200° C., or less than 150° C., or lessthan 100° C., or from 100° C. to 200° C., or from 200° C. to 300° C., orfrom 300° C. to 400° C., or from 400° C. to 500° C., or from 500° C. to600° C., or from 600° C. to 700° C., or from 700° C. to 800° C., or from800° C. to 900° C., or from 900° C. to 1000° C., or from 1000° C. to1100° C., or from 1100° C. to 1200° C., or from 1200° C. to 1300° C., orfrom 1300° C. to 1400° C., or from 1400° C. to 1500° C., or from 1500°C. to 1600° C. In some embodiments, a method of producing the cathode ofan electrochromic device comprises synthesizing hexagonal tungstentrioxide or pyrochlore particles by hydrothermal synthesis;size-reducing the hexagonal tungsten trioxide or pyrochlore particles bygrinding to produce crystalline hexagonal tungsten trioxide orpyrochlore nanostructures; and coating the tungsten trioxide orpyrochlore nanostructures on a substrate, wherein the substrate has aglass transition temperature less than 1000° C., or less than 900° C.,or less than 800° C., or less than 700° C., or less than 600° C., orless than 500° C., or less than 400° C., or less than 300° C., or lessthan 250° C., or less than 200° C., or less than 150° C., or less than100° C., or from 75° C. to 125° C., or from 125° C. to 175° C., or from175° C. to 225° C., or from 225° C. to 275° C., or from 275° C. to 325°C., or from 325° C. to 375° C., or from 375° C. to 425° C., or from 425°C. to 500° C., or from 500° C. to 600° C., or from 600° C. to 700° C.,or from 700° C. to 800° C., or from 800° C. to 900° C. In someembodiments, a method of producing the cathode of an electrochromicdevice comprises synthesizing hexagonal tungsten trioxide or pyrochloreparticles by hydrothermal synthesis; size-reducing the hexagonaltungsten trioxide or pyrochlore particles by grinding to producecrystalline hexagonal tungsten trioxide or pyrochlore nanostructures;and coating the tungsten trioxide or pyrochlore nanostructures on asubstrate, wherein the substrate has a softening point less than 1000°C., or less than 900° C., or less than 800° C., or less than 700° C., orless than 600° C., or less than 500° C., or less than 400° C., or lessthan 300° C., or less than 250° C., or less than 200° C., or less than150° C., or less than 100° C., or from 75° C. to 125° C., or from 125°C. to 175° C., or from 175° C. to 225° C., or from 225° C. to 275° C.,or from 275° C. to 325° C., or from 325° C. to 375° C., or from 375° C.to 425° C., or from 425° C. to 500° C., or from 500° C. to 600° C., orfrom 600° C. to 700° C., or from 700° C. to 800° C., or from 800° C. to900° C.

In some embodiments, a method of producing the cathode of anelectrochromic device comprises synthesizing hexagonal tungsten trioxideor pyrochlore particles by hydrothermal synthesis; size-reducing thehexagonal tungsten trioxide or pyrochlore particles by grinding toproduce crystalline hexagonal tungsten trioxide or pyrochlorenanostructures; and coating the hexagonal tungsten trioxide orpyrochlore nanostructures on a substrate, wherein the substrate isthicker than 50 microns.

In some embodiments, a method of producing the cathode of anelectrochromic device comprises synthesizing hexagonal tungsten trioxideor pyrochlore particles by hydrothermal synthesis; size-reducing thehexagonal tungsten trioxide or pyrochlore particles by grinding toproduce crystalline hexagonal tungsten trioxide or pyrochlorenanostructures; and coating the hexagonal tungsten trioxide orpyrochlore nanostructures on a substrate, wherein the substratecomprises an electrically conducting layer and outer substrate, and thematerial of the outer substrate is selected from the group consistingof: glass (e.g. soda lime glass or borosilicate glass), and plastic(e.g. polycarbonates, polyacrylics, polyurethanes, urethane carbonatecopolymers, polysulfones, polyimides, polyacrylates, polyethers,polyester, polyethylenes, polyalkenes, polyimides, polysulfides,polyvinylacetates and cellulose-based polymers).

In some embodiments, a method of producing the cathode of anelectrochromic device comprises synthesizing hexagonal tungsten trioxideor pyrochlore particles by hydrothermal synthesis; size-reducing thehexagonal tungsten trioxide or pyrochlore particles by grinding toproduce crystalline hexagonal tungsten trioxide or pyrochlorenanostructures; and coating the hexagonal tungsten trioxide orpyrochlore nanostructures on a substrate, wherein the substratecomprises an electrically conducting layer and outer substrate, and thematerial of the electrically conductive layer is selected from a groupconsisting of: transparent conductive oxides, thin metallic coatings,networks of conductive nanoparticles (e.g., rods, tubes, dots),conductive metal nitrides, and composite conductors.

In some embodiments, EC devices with hexagonal tungsten trioxide orpyrochlore cathodes have fast switching speeds. Not to be limited bytheory, the large channels in the crystal structure of hexagonaltungsten trioxide enables a high ionic mobility for the intercalatedions (e.g. Li+).

The electrochromic devices incorporating the nanostructures described inthis disclosure may also be particle-based electrochromic devices. Aparticle-based electrochromic device is an electrochromic structurewhere one or more of the functional layers is formed of nanoparticles ornanostructures, such as those described above. The functional layersinclude the transparent conductive layers, the electrodes (anode and orcathode), and the ion conductor. An electrochromic particle-based systemis one where the particles or nanoparticles in such a system are solidstate materials with an extended solid state crystal structure and havesubstitutable atoms such as metals and ligands that can be substitutedto tune the electrochromic properties. A unit cell of the crystalstructure is the smallest repeatable unit within that structure and canbe used both to describe the contents of the crystal and to estimate thenumber of atoms and/or unit cells in a particle of a given size. Thenumber of atoms/unit cells in a particle can be estimated based on knownbond lengths between different atoms and the positions of the atoms inthe unit cells. The electrochromic particles may range from 1-200 nm atthe largest and 10-50 nm as a more preferred range.

Although a range of electrochromic materials could be used inparticle-based electrochromic systems, there is a need for anode filmsthat can be prepared by simple low temperature single-step depositionprocesses to produce electrochromic electrodes (i.e., electrochromiccathodes, electrochromic anodes or electrochromic anodes and cathodes)with improved thermal stability, high optical clarity in theiras-deposited states, and that can be tuned via composition and filmthickness to adopt a wide variety of area charge capacities and opticalswitching properties.

In general, the particle-based systems may be tuned to obtainelectrochromic materials (EC systems) that reversibly change from atransparent state having a good T_(vis) to a dark color having a highcoloration efficiency. In various embodiments of this invention, theelectrochromic properties that may be tuned are:

-   -   a. Bleached state of material: Transparent, clear color    -   b. Dark state of material: The desired color can vary based on        the different purposes, but for EC windows the color may be        anything pleasing to the human eye in the dark state (e.g.        “night sky” grey-blue). Both of the electrodes (anode and        cathode) can contribute to the color of the dark state or only        one of the electrodes can be coloring. In the instance where        both anode and cathode are contribute to the color of the final        EC device, then the color tuning may be performed to match one        to the other to create an overall color for the dark state. The        color may be based on a standard such as a CIE L*a*b* value. In        particular, b* should be less than 10.    -   c. Coloration efficiency: A deep dark color is desired in the        dark state, as opaque as possible. Therefore, a high coloration        efficiency is desired.    -   d. Switching speed: A fast switching speed between oxidized and        reduced states, where the transparent state is 5% or less in the        transparent state when switched and the dark state is at least        65% darkened.    -   e. Voltage matching of the anode and cathode in the final EC        device.    -   f. Anode: Want dark colored oxidized state and a        clear/transparent reduced state    -   g. Cathode: Want clear/transparent oxidized state and dark        colored reduced state

Both anodic and cathodic electrochromic particle-based materials may betuned for any of the above properties using methods of substitutingmetals and ligands. Of particular interest is tuning the color of theelectrochromic particle-based materials. The particle-based cathodematerial may be any of the tungsten oxide nanostructures described inthis disclosure. The particle-based anode materials may be any materialcompatible with the other materials selected as part of theelectrochromic device, from a chemical compatibility standpoint as wellas from a device functionality standpoint. Chemically the materialsshould be compatible in that they do not detrimentally interact with oneanother. From a device functionality standpoint the device materials canbe selected to provide a device that performs within parametersdetermined to be optimal for the various products into which it may beintegrated. For example the anode and cathode may be selected to havedark-state colors that combine to provide a desired color. In anotherexample the materials may be selected to provide a particular switchingspeed or coloration efficiency.

Prussian blue (iron(III) hexacyanoferrate(II)) and Prussian blueanalogues (metal hexacyanometallates) are examples of electrochromicmaterials that could be used for the anodes in electrochromic devices.Prussian Blue is the commonly used name for Iron Hexacyanoferrate orFe₄[Fe(CN)₆]₃.xH₂O (x is commonly described as a range 10-14). APrussian Blue Analog=(M¹, M²)_(x)[M³,M⁴(CN)_(6−y)L_(y)]_(z).

In the formation of Prussian Blue, the addition of Fe³⁺ tohexacyanoferrate(II) in water simultaneously precipitates the productwith a quantitative yield as agglomerates of nanocrystals (10-20 nm).Cyanide-bridging between the two octahedral Fe ions of Prussian Blueextends to a cubic framework, containing water and some of alkalinecations in the pores. This open-framework enables the Prussian blueiron-cyanide complex to perform a charge/discharge process of mobilecations without causing significant stress to the scaffold. In addition,a highly intense blue color stemming from the intervalentcharge-transfer between Fe²⁺ and Fe³⁺ centers is beneficial in achievinghigh coloration efficiency at its dark state color. Upon the chemical-or electrochemical-reduction of Fe³⁺ to Fe²⁺, the material readily losesits blue color and turning to translucent state, which affords a greatclarity at the bleached state. In one embodiment, the anode material maybe a Prussian blue analog possessing relatively high colorationefficiency at relatively low voltages, and having a hue (or a CIE L*a*b*value) that provides the desired dark-state color in the electrochromicdevice.

Electrochromic behavior of Prussian blue thin films have been studiedwith aqueous or non-aqueous electrolyte solutions with various mobilecations such as H⁺, Li⁺, Na⁺, K⁺, and NH₄ ⁺. It is well known that itperforms fast and stable switching between blue and colorless states,with only slight deterioration over many cycles. In addition, thevoltage range closely matches to that of cathodic WO₃, which affordsfairly fast and stable switching in the devices. Indeed, excellentcell-durability over 20,000 cycles has been reported from anelectrochromic device composed of a Prussian blue anode and a WO₃cathode that were laminated with a proton-based ion conductor betweenthem.

Despite the fast and stable electrochromic switching of Prussian blue,the dark state color is aesthetically less than ideal for someapplications such as residential, commercial, or automobile windows. Forexample, when matched to a WO₃ cathode in an electrochromic device, thedevice colors to an intense blue at the dark state, representing a largeb* (b-star) measurement as defined in the “Lab” color space. A Lab colorspace is a color-opponent space with dimension L for lightness and a*and b* for the color-opponent dimensions, based on nonlinearlycompressed (e.g. CIE XYZ color space) coordinates. To improve the colorto a different regime (e.g., to reduce b* and increase L in the L*,a*,b*color space), it has been proposed to substitute a range of transitionmetals for iron to form various Prussian blue analogues.

Substitutions of metals or ligands will change the size of the unitcells in a somewhat predictable manner. For example, we can substitutemetals in tungsten oxide materials or Prussian blue analog materials,and as we substitute those metals the bond lengths between metals andligands may change somewhat. As a consequence, unit cell sizes withinthe particles may change to some extent.

Prussian Blue is a framework structure with octahedrally coordinatedmetals surrounded by cyanide ligands. Due to the directional nature ofthe cyanide ligand, the structure can be further described as havingmetal atoms octahedrally coordinated by the cyanide carbon atom andother metal atoms octahedrally coordinated by the cyanide nitrogen atomcontinuing in 3 dimensions.

Prussian Blue Analog as used herein is a broad term to describe anyframework structure similar to Prussian Blue where metal atoms arecoordinated octahedrally by ligands arranged in a face-centered cubic orsimilar symmetry. Often the ligands are cyano (CN) groups (y=0) but thecyano groups can be replaced by other ligands. The substituted ligand Lcan be any ligand from the spectroelectrochemical series but inparticular any ligand that is similar to a cyano (CN) group in terms ofsize, electronic properties, and/or geometry.

There are some types of Prussian Blue Analogs that have well-knownnames, such as those including the Nitroprusside anion [Fe(CN)₅NO]²⁻ andIron Nitroprusside (Iron Pentacyanonitrosylferrate=Fe[Fe(CN)₅NO]), whichhas a similar structure to Prussian Blue with 1 cyanide group replacedby a nitrosyl group.

Prussian Blue Analogs refer to embodiments where metals, ligands, bothmetals and ligands simultaneously, precursors, solvents and generalsynthetic methods have been manipulated with the intent of modifyingcolor, durability, transmissivity, switching speed and/or particle size,ease of dispersing in a solvent, ease and quality of coating adispersion, ease or cost of synthesizing a material, temperature,environment of preparation or other meaningful synthesis, materials,formulation and device properties, as necessary.

In one embodiment, this involves the substitution of metals or ligandsin Prussian blue analogs having the formula (M1, M2)x[M3,M4(CN)6-yLy]z.Any of the metals 1-4 may be substituted in any variation, either withor without iron (Fe) as one of the metals. There may be a single metalused in the analog or up to 4 different metals in a mixed metal analog.The substitution of the metal bonded to the carbon or analogous atominside of the brackets may have different effects than the substitutionof the metals on the outside of the brackets (the Nitrogen or analogousatom of the ligand.) Metals that may be use in the substitution includeany of the transition metals, and particular examples include titanium,manganese, ruthenium, vanadium, nickel, cobalt, copper, palladium,indium, cadmium, chromium, molybdenum, osmium, platinum, rhenium,rhodium, silver, zinc, and zirconium.

In one embodiment, the metals were varied in the Prussian Blue analogM[FexCr1-x(CN)6]. The metal M was varied between iron (Fe2+), Cobalt(Co2+), Copper (Cu2+), and manganese (Mn2+). For each of these metal Mvariations the mole fraction of each hexacyanometallate (the Fe and Crinside of the brackets) was varied as the following ratio of Fe to Cr: 0to 1, 0.2 to 0.8, 0.4 to 0.6, and 0.8 to 0.2. This resulted in a widerange of colors for the particle-based Prussian blue analog dispersion.Colors observed included reds, browns, blues, and clear. These were eachreduced using Na2SO3 to colors including reds, oranges, yellows, andwhites. This experiment demonstrates the color tuning methodology thatmay be performed to identify particles having different colors in bothoxidized and reduced states.

In another embodiment, the metals were varied in the Prussian Blueanalog M[Mn(CN)6] which demonstrated different shades of brown in theoxidized state and white in the reduced state. M was varied withsubstitutions of Cobalt, Manganese, Copper, and Iron and chemicallyreduced by Na2SO3. The Cu[Mn(CN)6] version showed a promising oxidizedstate color of very dark brown and a reduced state of white, which maybe of value to use in an electrochromic device used for windows.

Another color-tuning approach that was tried was the “core-shell” methodwere a “core” solid particles of Prussian Blue, Mn[Fe(CN)₆],Zn[Fe(CN)₆], Ni[Fe(CN)₆], and Co[Fe(CN)₆]. Each of these “core”compounds were mixed with cations of “shell” metals including silver,cerium, cobalt, copper, chromium, iron (II and III), Indium, Manganese,and titanium (II and III.) The cations on the outside of theelectrochromic particles had an effect on the color of the oxidized andreduced solution. In the oxidized state the colors ranged from browns,to oranges, to yellows, to whites, to greens, and to blues.

In another embodiment, the ligands (L) may be substituted in combinationwith variations of the metals or independently of the metalsubstitution, and up to five of the ligands (L) may be substituted withligands other than the cyano (CN) groups. The ligands substituted may beany from the spectroelectrochemical spectrum, and more particularly anythat are high on the spectroelectrochemical spectrum. In specificembodiments, the ligands may be substituted with ligands that aresimilar in structure, both electronically and geometrically, to a cyano(CN) group such as Nitrosyl (NO), Carbonyl (CO), Halide (Cl, Br, F, I),isocyanate, and thiocyanide.

The ion conductor material used in particle-based electrochromic devicesin one embodiment may be produced from a liquid formulation thatcomprises an electrolyte solvent or plasticizer, a polymerizable monomeror set of monomers, an optional polymerization initiator, and a saltsuch as a lithium salt or an acid. The formulation may also compriseother additives to promote device performance such as pH buffers, UVstablizers, and the like. In another embodiment, the ion-conducting filmis produced from the ion conducting formulation by depositing the liquidformulation with the anode film, cathode film, or both films in asufficient quantity to form a continuous pre-crosslinked film having auniform thickness between 50 and 500 microns between the anode andcathode plates. This assembly may then placed in a vacuum laminator andheated under vacuum to form a sealed assembly. Polymerization of themonomer/comonomer may be initiated either thermally or photochemically.In one embodiment, any thermal processing of the device, particularlyone where plastic is as the substrate, is below the temperature of 200°C., and more particularly 150° C., and even more particularly 100° C.

Alternatively, free standing fully formulated ion-conducting films maybe used in place of the crosslinking IC formulation or the liquid ICformulation may be used in a “cast in place” process where a pre-formedcavity between the anode and cathode is produced (edge sealed) and theformulation is forced into this cavity through fill ports. Typicalmonomers used in these formulations are polar organic olefins such asacrylates, or other well-known polymerization systems such as silicones,urethanes and the like.

In an alternative embodiment, the structure of the electrochromic devicemay employ a symmetric electrode assembly, where each of the electrodelayers include a mixture of both anode and cathode electrochromicparticles.

In another embodiment, the EC device may be formed by a combination ofboth anodic and cathodic particles dispersed in a single layer betweentwo conductive layers where at least one of the anodic or cathodicparticles are transparent in both oxidized and reduced states so thatthe color is created by only one of the anodic or cathodic particles.

Particle-based formulations for the different components inelectrochromic devices allows for alternative techniques for making ECdevices having the components described above including the anode,cathode, ion conductor, and the transparent conductive layers. Aparticle-based coating technology may also enable novel devicearchitectures to exploit the potential for greatly reduced devicecomplexity, growing EC films post-deposition (of particular value forcurved applications), and post-device completion defect repair.

In one embodiment the particle-based devices and techniques may bemixed-particle films, such as anode materials mixed with cathodematerials to produce a film that functions as both. In anotherembodiment the mixed particle films may be formed of non-electrochromicparticles mixed with electrochromic particles in a binder material toenhance specific properties, where the non-electrochromic particles maybe charge sequestration particles or additives to increase the ionic orelectronic conductivity of the device. The binder may be an organicmaterial that is both adhesive and ion-conducting. The transparentconductive layer (TCL) may also be particle-based and be incorporatedinto an adhesive film. The TCL particles may be approximately 2 micronsand create a resulting TCL film having a sheet resistance of about 50ohm/square to about 100 ohm/square. A particle based TCL with hightransparency and low haze but with low conductivity can also be used inthese types of systems due to the thinness of the TCL's. This is becauseany total conductivity can be achieved by layering the TCL layers. ForExample, 10 stacked 5 layer devices with TCL films having 250 ohm/sqwould have net 25 ohm/sq resistance. Thus, exceptional film performancewith relatively low volumetric charge capacity—and thus less need for ahigh conductivity TCL. This is valuable because the high conductivityTCL's are more expensive.

An example of a mixed-particle device may have the TCL adhesive filmsandwiching an adhesive ion conducting film which incorporates bothanode and cathode particles. Alternatively there may be two adhesive ionconducting films sandwiched between the TCL adhesive film, where one ofthe adhesive ion conducting films incorporates the anode material andthe other adhesive ion conducting film incorporates the cathodematerial. There may be more than two of the electrode and ion conductingadhesive films present in these types of devices in order to providemultiple discrete electrochromic layers. Roll to roll processing usingflexible films would enable efficient processing of such devices.

EXAMPLES

The following non-limiting examples are provided to further illustratethe present disclosure. It should be appreciated by those of skill inthe art that the techniques disclosed in the examples that followrepresent approaches the inventors have found function well in thepractice of the disclosure, and thus can be considered to constituteexamples of modes for its practice. However, those of skill in the artshould, in light of the present disclosure, appreciate that many changescan be made in the specific embodiments that are disclosed and stillobtain a like or similar result without departing from the spirit andscope of the disclosure.

Example 1 Hydrothermal Synthesis of Hexagonal Tungsten TrioxideNanostructures

FIG. 3a shows an example x-ray diffraction (XRD) pattern of hexagonaltungsten trioxide particles prepared using hydrothermal synthesis. ThisXRD pattern of the as-synthesized product may be fit to a crystalstructure of the space group P6/mmm (#191), where the lattice parametersare a=b=approximately 7.3 (Angstroms), and c=approximately 3.9(Angstroms). The hexagonal tungsten trioxide particles were preparedaccording to the following procedure.

A 125 mL steel autoclave vessel with a Teflon insert is used. 5.0 g ofNa₂WO₄*2H₂O and 1 g of NaCl is added to 45 ml of DI H₂O. The pH ismonitored, and the starting pH is typically 9.1 to 9.3. 3M HCl israpidly added, until the pH is equal to 1.5, and the solution turns alight green color. The reaction mixture is then loaded into theautoclave vessel, and heated to 180° C. for 6 hours.

After the reaction products cool to room temperature, the supernatantliquid is discarded, and the precipitate product is collected into acentrifuge tube using DI water. DI water is used to dilute the productto a total of about 45 mL, and then centrifuged at 4500 RPM for 4 min.The supernatant is again discarded, and DI H₂O is added to theprecipitate to get 25 mL total volume. A second centrifuge procedure isperformed at 4500 RPM for 4 min. The supernatant is again discarded, andthe centrifuge procedure is repeated two more times, diluting each timewith isopropanol. After decanting the isopropanol, the centrifuge tubesare dried in a vacuum environment. After drying, the powder is groundwith a mortar and pestle and is further dried before the XRD pattern inFIG. 3a was taken. The yield of the hexagonal tungsten trioxide fromthis process is typically 3.2 (+/−0.1) g.

The x-ray diffraction (XRD) pattern in FIG. 3a shows narrow peaks,indicating a high degree of crystallinity. Samples were analyzed using aBruker D8 Advance diffractometer employing CuKα radiation. Scans weremade in Bragg-Brentano geometry using a Ni filter between 5-110° 2Θ witha step size of 0.01°. Intensities of the (100), (001) and (200) peaksindicate that the crystallinity does not have a preferred orientation.In contrast, nanowires would typically show a preferred orientation,indicating that the material formed does not have the crystallinestructure of nanowires.

Example 2 Hydrothermal Synthesis of Pyrochlore Nanostructures

FIG. 3b shows an example x-ray diffraction (XRD) pattern of pyrochloreparticles prepared using hydrothermal synthesis. This XRD pattern of theas-synthesized product may be fit to a crystal structure of the spacegroup Fd-3m,(#227) where the lattice parameters are a=b=c approximately10.3 (Angstroms), The pyrochlore particles were prepared according tothe following procedure.

A 2 L autoclave vessel with a Glass insert is used. 80.0 g ofNa₂WO₄*2H₂O and 16 g of NaCl is added to 720 ml of DI H₂O. The pH ismonitored, and the starting pH is typically 10.1 to 10.3. 3M HCl israpidly added, until the pH is equal to 3.5. The reaction mixture isthen loaded into the autoclave vessel, and heated to 200° C. for 12hours.

After the reaction products cool to room temperature, the supernatantliquid is discarded, and the precipitate product is collected into acentrifuge tube using DI water. DI water is used to dilute the productto a total of about 500 mL, and then centrifuged at 4500 RPM for 4 min.The supernatant is again discarded, and DI H₂O is added to theprecipitate to get about 500 mL total volume. A second centrifugeprocedure is performed at 4500 RPM for 4 min. The supernatant is againdiscarded, and the centrifuge procedure is repeated again withisopropanol to a similar volume. After decanting the isopropanol, thecentrifuge tubes are dried in a vacuum environment. After drying, thepowder is ground with a mortar and pestle and is further dried beforethe XRD pattern in FIG. 3b was taken. The yield of the pyrochlore fromthis process is typically 20 (+/−0.1) g.

The x-ray diffraction (XRD) pattern in FIG. 3b shows narrow peaks,indicating a high degree of crystallinity. Samples were analyzed using aBruker D8 Advance diffractometer employing CuKα radiation. Scans weremade in Bragg-Brentano geometry using a Ni filter between 5-110° 2Θ witha step size of 0.01°.

Example 3 Size Reduction of Hexagonal Tungsten Trioxide Nanostructures

FIG. 4a shows an XRD pattern of the hexagonal tungsten trioxide“starting material” (i.e. the as-synthesized material as described inExample 1), and the materials after size reducing and coating on asubstrate. Samples were analyzed using a Bruker D8 Advancediffractometer employing CuKα radiation. Scans were made inBragg-Brentano geometry using a Ni filter between 5-110° 2Θ with a stepsize of 0.01°. In this example, the dried powder (as described inExample 1) is size-reduced by grinding using an agitator bead mill. Themill has 80 mL bowls with ZrO₂ liners. The milling media are 0.1 mmdiameter ZrO₂ balls. The primary particle size of the starting materialis approximately between 5 and 500 nm, however, agglomerates from 1 to20 microns are also observed.

6.4 (+/−0.1) g of hexagonal tungsten trioxide material to besize-reduced by milling (e.g., product from 2 reaction batches using thesynthetic procedure described in Example 1) is added to 30 mL of IPA(isopropanol) and 100 (+/−1) g of 0.1 mm ZrO₂ balls, in the bowl of themill. The milling cycle parameters are 500 RPM for 3 min, followed by5-9 min of rest time (to allow the mill bowls to cool). The cycle isrepeated 20 times, for a total of 1 hour active milling time. Theformulation is then extracted from milling bowls and filtered toseparate the milling media from the formulation.

Additional IPA is then added to the milling bowls and the mixture isshaken and sonicated to remove any remaining hexagonal tungsten trioxideparticles from the milling balls and bowl. This process is continueduntil a total formulation volume of 30-40 mL is achieved. After thefinal formulation volume is achieved, the slurry is characterized by TGAto determine weight %. An aliquot of the formulation is diluted andcharacterized by dynamic light scattering (DLS) for particle sizeanalysis.

In this example, after milling, the hexagonal tungsten trioxidenanostructures are coated onto a substrate using slot die coating. Thedie lip to substrate gap is from 80 microns, and the gap between the diehalves is approximately 100 microns. The wet coating thickness is 37microns. The concentration by mass of the solid nanostructures isapproximately 10%, and the dry film thickness is approximately 600 nm to1 micron. The coating speed is approximately 300 cm/min. The film wascoated and dried at room temperature and 15% relative humidity.

The XRD pattern in FIG. 4a shows the size-reduced nanoparticles coatedon an FTO coated glass substrate. The background XRD pattern from theFTO coated glass substrate shows a broad background signal at lowangles, and at 2Θ of around 25° from the amorphous glass substrate, anda set of sharp peaks associated with the FTO (e.g., at 2Θ approximately26.5°, 38°, 51.5°, 61.5° and 65.5°). The scan taken from thenanoparticle coated substrate shows the same broad peaks and FTO peaksfrom the substrate superimposed with the peaks from the hexagonaltungsten trioxide. The hexagonal tungsten trioxide peak positions in thecoated sample are very similar to the peak positions taken from thesample directly after hydrothermal synthesis and washing; no additionalpeaks are seen indicating that the crystal structure was not alteredduring the milling process. Peak widths however have clearly broadenedindicating that the particle size has been altered in comparison to theas-synthesized particle size. Analysis of the XRD pattern after sizereduction indicates that the average crystallite size is approximately150 nm.

An example of a hexagonal tungsten trioxide particle size distributionafter milling, washing, and separating from the washing contaminants isshown in FIG. 4b . The mean particle size in this distribution is 144nm, and the PDI is 0.144, as measured by DLS.

Example 4 Size Reduction of Pyrochlore Nanostructures

FIG. 5a shows an XRD pattern of the pyrochlore “starting material” (i.e.the as-synthesized material as described in Example 2), and thematerials after size reducing and coating on a substrate. Samples wereanalyzed using a Bruker D8 Advance diffractometer employing CuKαradiation. Scans were made in Bragg-Brentano geometry using a Ni filterbetween 5-110° 2Θ with a step size of 0.01°. In this example, the driedpowder (as described in Example 2) is size-reduced by grinding using anagitator bead mill. The mill has 80 mL bowls with ZrO₂ liners. Themilling media are 0.1 mm diameter ZrO₂ balls. The primary particle sizeof the starting material is approximately between 5 and 500 nm, however,agglomerates from 1 to 20 microns are also observed.

6.4 (+/−0.1) g of pyrochlore material to be size-reduced by milling(e.g., product from 2 reaction batches using the synthetic proceduredescribed in Example 2) is added to 30 mL of DI water and 100 (+/−1) gof 0.1 mm ZrO₂ balls, in the bowl of the mill. The milling cycleparameters are 500 RPM for 3 min, followed by 5-9 min of rest time (toallow the mill bowls to cool). The cycle is repeated 20 times, for atotal of 1 hour active milling time. The formulation is then extractedfrom milling bowls and filtered to separate the milling media from theformulation.

Additional DI water is then added to the milling bowls and the mixtureis shaken and sonicated to remove any remaining pyrochlore particlesfrom the milling balls and bowl. This process is continued until a totalformulation volume of 30-40 mL is achieved. After the final formulationvolume is achieved, the slurry is characterized by TGA to determineweight %. An aliquot of the formulation is diluted and characterized bydynamic light scattering DLS for particle size analysis.

In this example, after milling, the pyrochlore nanostructures are coatedonto a substrate using slot die coating. The die lip to substrate gap isfrom 80 microns, and the gap between the die halves is approximately 100microns. The wet coating thickness is 37 microns. The concentration bymass of the solid nanostructures is approximately 10%, and the dry filmthickness is approximately 600 nm to 1 micron. The coating speed isapproximately 300 cm/min. The film was coated and dried at roomtemperature and 15% relative humidity.

The XRD pattern in FIG. 5a shows the size-reduced nanoparticles coatedon an ITO/TTO coated glass substrate. The background XRD pattern fromthe ITO/TTO coated glass substrate shows a broad background signal atlow angles, and at 2Θ of around 25° from the amorphous glass substrate,and a set of sharp peaks associated with the ITO/TTO (e.g., at 2Θapproximately 30.2°, 35.1°, 50.5°, and 60°). The scan taken from thenanoparticle coated substrate shows the same broad peaks and ITO/TTOpeaks from the substrate superimposed with the peaks from thepyrochlore. The pyrochlore peak positions in the coated sample are verysimilar to the peak positions taken from the sample directly afterhydrothermal synthesis and washing; no additional peaks are seenindicating that the crystal structure was not altered during the millingprocess. Peak widths however have clearly broadened indicating that theparticle size has been altered in comparison to the as-synthesizedparticle size. Analysis of the XRD pattern after size reductionindicates that the average crystallite size is approximately 56 nm.

An example of a pyrochlore particle size distribution after milling,washing, and separating from the washing contaminants is shown in FIG.5b . The mean particle size in this distribution is 122 nm, and the PDIis 0.280, as measured by DLS.

Example 5 Electrochemical and Electrochromic Devices IncorporatingHexagonal Tungsten Trioxide Nanostructure Thin Film Cathodes

Hexagonal tungsten trioxide nanostructures and inks are prepared by themethods described in Ex. 1 and Ex. 3.

Devices requiring optical characterization (i.e. devices producing thedata shown in FIGS. 6a, 6b, 7a and 7b ) were prepared by coating thehexagonal tungsten trioxide particles (without carbon black or PVDF) on20×20 mm² FTO coated glass substrates. The electrochromic testing wasperformed in a propylene carbonate+1 M LiTFSi(Bis(trifluoromethane)sulfonimide lithium) solution with a Li counterelectrode.

FIG. 6a shows transmission spectra of a hexagonal tungsten trioxideelectrochromic half-cell (or substrate) in the bleached and dark states.The transmission in the bleached state at a wavelength of 633 nm is90.5% compared to 1.85% in the dark state. The transmission at 550 nm is91.25% in the bleached state and 8.83% in the dark state.

FIG. 6b shows transmission spectra of a pyrochlore electrochromichalf-cell (or substrate) in the bleached and dark states. Thetransmission in the bleached state at a wavelength of 633 nm isapproximately 85% compared to approximately 4% in the dark state. Thetransmission at 550 nm is approximately 83% in the bleached state andapproximately 12.5% in the dark state.

FIG. 7a shows the fade for a monoclinic perovskite WO₃ half-cellcompared to a pyrochlore tungsten oxide half-cell and a hexagonaltungsten trioxide half-cell. The fade refers to the percent change incapacity between cycles 2 and 23. The fade for the monoclinic perovskiteWO₃ device is about −13.6%, while the fade for the pyrochlore tungstenoxide half-cell is only −7.3% and fade for the hexagonal tungstentrioxide half-cell is only −3.5%. The fade is a measure of durability,and this data supports the improved durability of pyrochlore andhexagonal tungsten trioxide compared to monoclinic perovskite tungstentrioxide.

FIG. 7b shows the switching rate for a monoclinic perovskite WO₃half-cell compared to a pyrochlore tungsten oxide half-cell and ahexagonal tungsten trioxide half-cell. The switching rate refers to thereduction in capacity observed when the material is reduced at a currentI equal to the initial Q (C)/120 s rather than at 25×10⁻⁶ Amp. Theswitching rate is similar to the C-rate commonly used for batteries. Theswitching rate for the monoclinic WO₃ half-cell is about −22%, while theswitching rate for the pyrochlore tungsten oxide is −15% and theswitching rate for hexagonal tungsten trioxide device is only −7%. Notto be limited by theory, the switching rate is related to the ionicmobility of Li+ in the cathode, and this data supports the improvedionic mobility of Li+ in the pyrochlore and hexagonal tungsten trioxidecompared to monoclinic perovskite tungsten trioxide.

What is claimed is:
 1. A method of manufacturing a thin film comprising:providing a plurality of crystalline hexagonal tungsten trioxideparticles; size-reducing the crystalline hexagonal tungsten trioxideparticles by grinding to produce crystalline hexagonal tungsten trioxidenanostructures; and coating the crystalline hexagonal tungsten trioxidenanostructures onto a substrate to produce a thin film.
 2. The method ofclaim 1, wherein the crystalline hexagonal tungsten trioxide particlesare produced via hydrothermal synthesis.
 3. The method of claim 1,wherein the thin film does not comprise a binder material.
 4. The methodof claim 1, wherein the substrate comprises a material with a softeningpoint less than 600° C.
 5. The method of claim 1, wherein the substratecomprises a material with a softening point less than 300° C.
 6. Themethod of claim 1, wherein the thin film is a layer in an electrochromicdevice.
 7. The method of claim 1, wherein the thin film is anelectrochromic cathode layer in an electrochromic device.
 8. The methodof claim 1, wherein the substrate comprises: an electrically conductivelayer, and an outer substrate.
 9. The method of claim 8, wherein theelectrically conductive layer is selected from a group consisting of:transparent conductive oxides, thin metallic coatings, networks ofconductive nanoparticles (e.g., rods, tubes, dots), conductive metalnitrides, and composite conductors.
 10. The method of claim 8, whereinthe outer substrate is selected from a group consisting of: glass (e.g.soda lime glass or borosilicate glass), and plastic (e.g.polycarbonates, polyacrylics, polyurethanes, urethane carbonatecopolymers, polysulfones, polyimides, polyacrylates, polyethers,polyester, polyethylenes, polyalkenes, polyimides, polysulfides,polyvinylacetates and cellulose-based polymers).
 11. An electrochromicmulti-layer stack comprising: a thin film comprising crystallinehexagonal tungsten trioxide nanostructures; an electrically conductivelayer; and an outer substrate, wherein the thin film does not comprise abinder.
 12. The electrochromic multi-layer stack of claim 11, whereinthe crystalline hexagonal tungsten oxide nanostructures are produced viahydrothermal synthesis followed by size reduction via grinding.
 13. Theelectrochromic multi-layer stack of claim 11, wherein the transparentsubstrate comprises a material with a softening point less than 600° C.14. The electrochromic multi-layer stack of claim 11, wherein themulti-layer stack is incorporated into an electrochromic device.
 15. Theelectrochromic multi-layer stack of claim 11, wherein the thin film isan electrochromic cathode layer in an electrochromic device.
 16. Theelectrochromic multi-layer stack of claim 11, wherein the electricallyconductive layer is selected from the group consisting of: transparentconductive oxides, thin metallic coatings, networks of conductivenanoparticles (e.g., rods, tubes, dots), conductive metal nitrides, andcomposite conductors.
 17. The electrochromic multi-layer stack of claim11, wherein the outer substrate is selected from the group consistingof: glass (e.g. soda lime glass or borosilicate glass), and plastic(e.g. polycarbonates, polyacrylics, polyurethanes, urethane carbonatecopolymers, polysulfones, polyimides, polyacrylates, polyethers,polyester, polyethylenes, polyalkenes, polyimides, polysulfides,polyvinylacetates and cellulose-based polymers).